Family name Piyadej (Piyadej 
) , across the world, is an extremely rare cognomen. Much more frequently, Piyadej is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Piyadej | Thailand |
Gridtham, Chaikiturajai, Pongtankul, Ekawaravong, Kalyanamit, Vongchansilp, Pornpithaksuk, Wongsirikul, and Vijaranakorn