diff --git a/src/api.rs b/src/api.rs
index 9d5afc0..60d50af 100644
--- a/src/api.rs
+++ b/src/api.rs
@@ -150,11 +150,31 @@ struct SyncParams {
     limit: Option<i64>
 }
 
+#[derive(Serialize)]
+struct SyncConflict {
+    #[serde(rename(serialize = "type"))]
+    conf_type: String,
+    server_item: Option<item::SyncItem>,
+    unsaved_item: Option<item::SyncItem>
+}
+
+impl SyncConflict {
+    fn uuid<'a>(&self) -> String {
+        if let Some(ref item) = self.server_item {
+            item.uuid.clone()
+        } else if let Some(ref item) = self.unsaved_item {
+            item.uuid.clone()
+        } else {
+            panic!("SyncConflict should have either server_item or unsaved_item");
+        }
+    }
+}
+
 #[derive(Serialize)]
 struct SyncResp {
     retrieved_items: Vec<item::SyncItem>,
     saved_items: Vec<item::SyncItem>,
-    unsaved: Vec<item::SyncItem>,
+    conflicts: Vec<SyncConflict>,
     sync_token: Option<String>, // for convenience, we will actually always return this
     cursor_token: Option<String>
 }
@@ -164,27 +184,13 @@ fn items_sync(db: DbConn, u: user::User, params: Json<SyncParams>) -> Custom<Jso
     let mut resp = SyncResp {
         retrieved_items: vec![],
         saved_items: vec![],
-        unsaved: vec![],
+        conflicts: vec![],
         sync_token: None,
         cursor_token: None
     };
 
     let inner_params = params.into_inner();
 
-    // First, update all items sent by client
-    for mut it in inner_params.items.into_iter() {
-        // Always update updated_at for all items on server
-        it.updated_at = 
-            Some(chrono::Utc::now().to_rfc3339_opts(chrono::SecondsFormat::Millis, true));
-
-        if let Err(item::ItemOpError(e)) = item::SyncItem::items_insert(&db, &u, &it) {
-            // We can just return an error here
-            return error_resp(Status::InternalServerError, vec![e]);
-        } else {
-            resp.saved_items.push(it);
-        }
-    }
-
     let mut from_id: Option<i64> = None;
     let mut had_cursor = false;
 
@@ -200,13 +206,13 @@ fn items_sync(db: DbConn, u: user::User, params: Json<SyncParams>) -> Custom<Jso
         from_id = sync_token.parse().ok();
     }
 
-    // Then, retrieve what the client needs
+    // First, retrieve what the client needs
     let result = item::SyncItem::items_of_user(&db, &u,
         from_id, None, inner_params.limit);
 
     match result {
         Err(item::ItemOpError(e)) => {
-            error_resp(Status::InternalServerError, vec![e])
+            return error_resp(Status::InternalServerError, vec![e])
         },
         Ok(items) => {
             if !items.is_empty() {
@@ -226,21 +232,93 @@ fn items_sync(db: DbConn, u: user::User, params: Json<SyncParams>) -> Custom<Jso
                     }
                 }
                 
-                // Always set sync_token to equal cursor_token in this case
-                resp.sync_token = Some(next_from.to_string());
+                // Always keep sync_token unchanged in this case
+                // (this may change later when we save items)
+                resp.sync_token = inner_params.sync_token;
             } else {
                 if had_cursor {
                     // If we already have no item to give, but the client still holds a cursor
                     // Revoke that cursor, and make it the sync_token
+                    // (this may change later when we save items)
                     resp.sync_token = resp.cursor_token.clone();
                     resp.cursor_token = None;
                 } else {
                     // Pass the same sync_token back
-                    resp.sync_token = inner_params.sync_token.clone();
+                    // (this may change later when we save items)
+                    resp.sync_token = inner_params.sync_token;
                 }
             }
             resp.retrieved_items = items.into_iter().map(|x| x.into()).collect();
-            Custom(Status::Ok, Json(Response::Success(resp)))
         }
     }
+
+    // Then, update all items sent by client
+    let mut last_id: i64 = -1;
+    for mut it in inner_params.items.into_iter() {
+        // Handle conflicts 
+        let mut conflicted = false;
+        for y in resp.retrieved_items.iter() {
+            if it.uuid == y.uuid {
+                conflicted = true;
+                // We assume enc_item_key identifies an "item"
+                if it.enc_item_key == y.enc_item_key {
+                    // A sync conflict
+                    resp.conflicts.push(SyncConflict {
+                        conf_type: "sync_conflict".to_string(),
+                        server_item: Some(y.clone()),
+                        unsaved_item: None
+                    });
+                } else {
+                    // A UUID conflict (unlikely)
+                    resp.conflicts.push(SyncConflict {
+                        conf_type: "uuid_conflict".to_string(),
+                        server_item: None,
+                        unsaved_item: Some(it.clone())
+                    })
+                }
+            }
+        }
+
+        // do not save conflicted items
+        if conflicted {
+            continue;
+        }
+
+        // Always update updated_at for all items on server
+        it.updated_at = 
+            Some(chrono::Utc::now().to_rfc3339_opts(chrono::SecondsFormat::Millis, true));
+
+        match item::SyncItem::items_insert(&db, &u, &it) {
+            Err(item::ItemOpError(e)) => {
+                return error_resp(Status::InternalServerError, vec![e]);
+            },
+            Ok(id) => {
+                last_id = id;
+                resp.saved_items.push(it);
+            }
+        }
+    }
+
+    if last_id > -1 {
+        // Update sync_token to the latest one of our saved items
+        resp.sync_token = Some(last_id.to_string());
+    }
+
+    // Remove conflicted items from retrieved items
+    let mut new_retrieved = vec![];
+    for x in resp.retrieved_items.into_iter() {
+        let mut is_conflict = false;
+        for y in resp.conflicts.iter() {
+            if x.uuid == y.uuid() {
+                is_conflict = true;
+            }
+        }
+
+        if !is_conflict {
+            new_retrieved.push(x);
+        }
+    }
+    resp.retrieved_items = new_retrieved;
+
+    Custom(Status::Ok, Json(Response::Success(resp)))
 }
\ No newline at end of file
diff --git a/src/item.rs b/src/item.rs
index 2d8fe99..6168b60 100644
--- a/src/item.rs
+++ b/src/item.rs
@@ -48,7 +48,7 @@ struct InsertItem {
     updated_at: Option<String>
 }
 
-#[derive(Serialize, Deserialize)]
+#[derive(Serialize, Deserialize, Clone)]
 pub struct SyncItem {
     pub uuid: String,
     pub content: Option<String>,
@@ -101,7 +101,16 @@ impl SyncItem {
             })
     }
 
-    pub fn items_insert(db: &SqliteConnection, u: &user::User, it: &SyncItem) -> Result<(), ItemOpError> {
+    pub fn find_item_by_uuid(db: &SqliteConnection, u: &user::User, i: &str) -> Result<Item, ItemOpError> {
+        lock_db_read!()
+            .and_then(|_| {
+                items.filter(owner.eq(u.id).and(uuid.eq(i)))
+                    .first::<Item>(db)
+                    .map_err(|_| "Database error".into())
+            })
+    }
+
+    pub fn items_insert(db: &SqliteConnection, u: &user::User, it: &SyncItem) -> Result<i64, ItemOpError> {
         // First, try to find the original item, if any, delete it, and insert a new one with the same UUID
         // This way, the ID is updated each time an item is updated
         // This method acts both as insertion and update
@@ -133,7 +142,10 @@ impl SyncItem {
                 updated_at: it.updated_at.clone()
             })
             .execute(db)
-            .map(|_| ())
-            .map_err(|_| "Database error".into())
+            .map_err(|_| "Database error".into())?;
+        std::mem::drop(_lock);
+
+        Self::find_item_by_uuid(db, u, &it.uuid)
+            .map(|i| i.id)
     }
 }
\ No newline at end of file