Worldwide, Gustain (Gustain 
) is a rare masculine forename. The first name Gustain is characteristic of Sub-Saharan Africa, particularly the Democratic Republic of the Congo, where it is a rare masculine name. Very seldom, Gustain is the last name as well as the forename.
| VARIANT | COUNTRY |
|---|---|
| Gustain | Germany, United States, India, Canada, Democratic Republic of the Congo |