There is little information regarding the extent of HIV infection among women. Since late 1985. members of the Arms' Reserve Components have been routinely tested for HIV. providing an opportunity to measure directly the prevalence and incidence density of infection in a military-associated population with limited military contact. We evaluated the presalence among 122.195 women, and directly measured the incidence density among 96.001 women followed for 247.872 person-years. The overall prevalence was 0.65 (per 1000). and the incidence density was 0.12 (per 1000 person years follow-up). Several demographically defined groups, including minority, women. had elevated levels of infection. The incidence densities of infection between early and late in the testing program were compared, and no evidence of acceleration or deceleration was observed.