They will be deleted from both collections. If you want to delete the collection and _only_ items that are not in any other collections, open the collection you want to delete, tag all items with some tag (e.g. "temp"; you can do this by creating a "temp" tag on one of the items, then drag all items to the tag in the tag selection pane), delete just the collection (without deleting the items), go to Unfiled special collection and delete all the items tagged with "temp". You can then delete the "Temp" tag. It's a bit roundabout, but it should work.

Thanks, this is useful, hopefully, the function can be enhanced in future releases

(please avoid tagging people -- aurimas hasn't done any work with Zotero for year, e.g. and devs read all threads)

There's a workaround you could use, but it's a bit involved:

- Tag all items in "Unfiled" with a tag (say, unfiled)*
- Create a saved search for Collection is [your collection] and Tag is NOT [unfiled] with match all and only top level items
- Tag all items in that saved search with another tag (say, to remove)
- filter by that tag in your collection and press delete (or right-click-->Remove from collection).

* I really wish we had Unfiled as an available search condition. Would make things so much easier