How many missions do you have to complete to unlock other islands in "Grand Theft Auto: San Andreas?"

The cities of San Fierro and Las Venturas may be visited as soon as the game is started, although doing so will attract the attention of the police. To safely visit these cities, missions 28 (for San Fierro) and 59 (for Las Venturas) must be completed.

In order to safely leave the starting city of Los Santos and access San Fierro, you must complete the mission titled "The Green Sabre" given by Sweet, which is mission number 28. To visit Las Venturas, you must complete the mission titled "Yay ka-boom-boom" given by Wu Zi Mu, which is mission number 59.