Family name גאיוס (Gaj 
, Gaius 
, Qay 
) , all around the world, is a common surname. The surname גאיוס is habitual in Suriname, where it is quite a rare surname, Poland, and Papua New Guinea. In absolute terms, it most frequently occurs in Nigeria, Poland, and India. Also, גאיוס is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Gaj | Poland, Italy, Nigeria, United States, India |
| Gaius | Nigeria, Papua New Guinea, Cameroon, India, Democratic Republic of the Congo |
| Qay | Germany, Pakistan, Indonesia, United States, Malaysia |
| גאיוס | Israel |