In all the world, Koster-Seidl (Koster-Seidl 
) is an extremely rare unknown gender forename. Much more frequently, Koster-Seidl is the last name as well as the forename. Parts of the name also exists independently as a last name Koster, and a last name Seidl.
| VARIANT | COUNTRY |
|---|---|
| Koster-Seidl | Germany |