In this minimal risk protocol, up to 400 asymptomatic HIV-infected patients and 75 HIV-infected patients with AVN will have MRI scans of the hips in order to determine (1) if avascular necrosis (AVN) of the hip can be identified by MRI scans in HIV-infected patients, and (2) to follow the natural history of asymptomatic and symptomatic AVN of the hip. Study procedures include MRI of the hip, a minimal risk imaging study, and phlebotomy.