MacCulloch played four seasons in the NBA before being forced to retire prematurely due to a genetic neuromuscular disorder that affected his feet, Charcot-Marie-Tooth disease. In his first two seasons with the Philadelphia 76ers, MacCulloch played reserve centre, averaging 9.4 minutes, 2.6 rebounds and just under 9 points in 56 and 63 games respectively from 1999 to 2001. In the 2001 off-season, he signed as a free agent with the New Jersey Nets and as their starting centre averaged 9.7 points and 6.1 rebounds a contest. MacCulloch was then traded back to the 76ers for the 2002–2003 season, in which he averaged just under 20 minutes, 9.1 points, and 4.7 rebounds a contest. Due to an inherited neurological disorder, Charcot-Marie-Tooth disease, which affects the peripheral nerves of the hands and feet he went on the injured reserve list at mid-season, did not play the following season, and announced his retirement in September 2004.