The purpose of this study was to evaluate the metabolic and cardiovascular benefits of continued metformin therapy for HIV-infected patients with lipodystrophy. Eligible subjects who participated in the 3-month randomized study received an additional 6-month open label metformin treatment extension. Nineteen of the 25 potential subjects were eligible to receive open label metformin based on preestablished safety and efficacy criteria. Insulin and glucose response to oral glucose challenge, cardiovascular disease risk markers (e.g. tissue plasminogen activator), weight, and anthropometric measurements were the primary outcome measures. Continued treatment with metformin resulted in further significant reductions in tissue plasminogen activator antigen levels (P = 0.02) and body mass index (P = 0.03). Reductions in insulin levels were sustained during the 6-month treatment extension. In addition, waist circumference decreased significantly in subjects continuing metformin treatment (P = 0.01). Metformin was well tolerated and no one discontinued treatment due to side effects. These data demonstrate a sustained benefit of metformin treatment to reduce hyperinsulinemia and certain markers of cardiovascular disease risk in patients with HIV infection and lipodystrophy.