Objective: To test the hypothesis that HIV infection impairs the beneficial effects of weight loss on insulin sensitivity, adipose tissue inflammation, and endoplasmic reticulum (ER) stress. Methods: A prospective clinical trial evaluated the effects of moderate diet-induced weight loss on body composition, metabolic function, and adipose tissue biology in women with obesity who were HIV-seronegative (HIV−) or HIV-positive (HIV+). Body composition, multiorgan insulin sensitivity (assessed by using a two-stage hyperinsulinemic-euglycemic clamp procedure with stable isotopically labeled tracer infusions), and adipose tissue expression of markers of inflammation, autophagy, and ER stress were evaluated in 8 HIV− and 20 HIV+ women with obesity before and after diet-induced weight loss of 6% to 8%. Results: Although weight loss was not different between groups (∼7.5%), the decrease in fat-free mass was greater in HIV+ than HIV− subjects (−4.4 ± 0.7% vs. −1.7 ± 1.0%, P < 0.05). Weight loss improved insulin sensitivity in adipose tissue (suppression of palmitate rate of appearance [Ra]), liver (suppression of glucose Ra), and muscle (glucose disposal) similarly in both groups. Weight loss did not affect adipose tissue expression of markers of inflammation or ER stress in either group. Conclusions: Moderate diet-induced weight loss improves multiorgan insulin sensitivity in HIV+ women to the same extent as women who are HIV−. However, weight loss causes a greater decline in fat-free mass in HIV+ than HIV− women.