Powerful drugs (highly active antiretroviral therapy, or HAART) have greatly improved survival and quality of life in patients infected with HIV. They also can produce troublesome side effects. One possible side effect, called lipodystrophy, deals with how the body makes and uses fat. Patients with lipodystrophy may have a wasting appearance because they lose fat from the face, arms, legs, and buttocks and gain it in the belly, breasts, and back of the neck. They can develop resistance to insulin (the hormone that allows cells to use sugar), diabetes, and a high triglyceride level. They also may have problems with their arteries (atherosclerosis) that increase the risk for stroke and heart attacks. Doctors now wonder whether drugs that affect insulin resistance and that are used to treat diabetes, such as rosiglitazone or metformin, may help prevent some of the problems associated with lipodystrophy.