A large proportion of human immunodeficiency virus antibody (HIV-Ab) positive male soldiers are considered to be at no identified risk (NIR) because they do not disclose histories of sexual activity with other men, intravenous drug use, blood transfusions, or sexual activity with persons at known high risk for HIV infection. A case-control study involving personal interviews with 26 NIR cases and 74 controls was conducted to determine if lifestyle information that might jeopardize a soldier's military career could be obtained from an Army population and to evaluate risk factors for prevalent HIV infection. Subjects consented to a voluntary, anonymous, and confidential interview containing information on demographic characteristics, medical history, drug use, and sexual behavior. Of 26 cases interviewed, 20 (76.9%) reported behaviors defined by the Centers for Disease Control (CDC) as risk factors for HIV infection, while 11 of 74 (14.9%) controls also reported such behaviors. This proportion of reclassified NIR cases was similar to that reported from the NIR case series study conducted by the CDC. Of the six (23.1%) cases who remained at NIR, all reported at least one of the following risks: a history of sexually transmitted diseases, sexual contact with prostitutes, or sexual activity with female partners which caused bleeding.(ABSTRACT TRUNCATED AT 250 WORDS)