Originally, Vice City was just a mission pack for GTA III
, by Thibaut
Thanks to an article published by Obbe Vermeij, former Technical Director at Rockstar North, we've learned a little more about the genesis of GTA: Vice City.
Indeed, this mythical entry was originally released on PS2 in 2002 as a mission pack for GTA III. The project retained this status for over six months during its development, before evolving into a full-fledged game.
What's more, the code from GTA III was largely reused on Vice City. The programmers only made a few changes.
Source: insiderockstarnorth.blogspot.com