The wide use of protease inhibitors (PI) as part of a highly active antiretroviral (HAART) regimen is associated with the development of several side effects. Among these, the development of avascular necrosis (AVN) of the bone is being reported more frequently and it has been related both to the use of PI and to HIV-1 infection itself. We report here a case of AVN of the bone in a patient taking the new PI lopinavir (LPV)/ritonavir (RTV) as part of a HAART regimen.