If the immigrant visa petition is approved, your brother or sister must wait for an immigrant visa number to become available according to the preference system. Because the number of immigrant visa numbers that are available each year is limited, they may not get an immigrant visa number immediately after the immigrant visa petition is approved. In some cases, several years could pass between the time USCIS approves the immigrant visa petition and the State Department provides an immigrant visa number. Because U.S. law also limits the number of immigrant visas available by country, they may have to wait longer if they come from a country with a high demand for U.S. immigrant visas.