BACKGROUND Osteopenia is prevalent in persons with human immunodeficiency virus (HIV) infection and is part of a normal sequence of aging in women. Most studies of bone mineral density (BMD) and HIV infection have focused on men or have lacked a comparison group of individuals without HIV infection with similar behavioral risk factors. METHODS We analyzed BMD in 495 middle-aged women (defined as women > or =40 years of age); 263 women had HIV infection, and 232 women were HIV-negative with behavioral risk factors similar to those of the HIV-positive group. RESULTS The median age of the women in the study was 44 years, 54% were black, and 92% had used illicit drugs. Femoral neck BMD and lumbar spine BMD were reduced in women with HIV infection, compared with women without HIV infection (femoral neck BMD, 1.01+/-0.13 g/cm2 vs. 1.05+/-0.13 g/cm2; P=.001; lumbar spine BMD, 1.21+/-0.17 g/cm2 vs. 1.24+/-0.17 g/cm2; P=.04). In addition to HIV infection, other factors independently associated with lower BMD in both sites were being older, not being black, and having a low body weight. In race-stratified multivariate analyses, HIV infection was associated with BMD only in non-black women. Among HIV-positive women, 84% had taken antiretrovirals, and 62% had taken protease inhibitors, but their use was not associated with BMD. Methadone treatment was also independently associated with reduced lumbar spine BMD. CONCLUSIONS Middle-aged women with HIV infection have reduced BMD, compared with women at similar risk for HIV infection, independent of antiretroviral use. Among HIV-positive women, those who are not black, who are underweight, and who use opiates may be at particular risk. Although the prevalence of reduced BMD in this cohort was higher among women with HIV infection than among those without (27% vs. 19%), the overall prevalence of reduced BMD was low, compared with national estimates and with previous studies involving HIV-positive women and men.