Although loss of lean body mass is a common complication of human immunodeficiency virus (HIV) infection that can occur across the disease trajectory, few studies have characterized the body composition of HIV-infected women. We used bioelectrical impedance analysis to characterize the body composition of HIV-infected (n = 56) and uninfected (n = 12) women who were matched on percentage of ideal body weight. The HIV-infected women did not differ from the uninfected women by height-adjusted fat mass or body cell mass. Intergroup comparisons among the HIV-infected women showed that underweight women had significantly less fat mass than did normal-weight women but did not significantly differ with respect to body cell mass. Among all HIV-infected women, CD4(+) lymphocyte count was positively correlated with fat mass (r = 0.32, P = 0.01) but not with body cell mass. No significant correlations were found between any body-composition parameter and plasma viral load. Our findings suggest that, unlike men, HIV-infected underweight women show a preferential loss of fat mass and a relative preservation of body cell mass. This altered pattern of weight loss may relate to higher premorbid fat stores in women and/or hormonal differences.