The characteristics and impact of pain were evaluated in a prospective cross-sectional survey of 438 ambulatory AIDS patients recruited from health care facilities in New York City. More than 60% of the patients reported 'frequent or persistent pain' during the 2 wks preceding the study. Patients with pain reported an average of 2.5 different pains. On the 0-10 numerical scale of the Brief Pain Inventory (BPI), mean pain intensity 'on average' was 5.4 (SD = 2.2; range = 0-10), and mean pain 'at its worst' was 7.4 (SD = 2.0; range = 1-10). The pain-related functional interference index (sum of the seven item BPI subscale) was 42.6 (SD = 17.2; range = 0.70). Demographic variables were not associated with the presence of pain, but the number of current HIV-related symptoms, treatment for HIV-related infections, and the absence of antiretroviral medications were significantly associated with the presence of pain. Female gender, non-Caucasian race, and number of HIV-related physical symptoms were significantly associated with pain intensity. Presence of pain and increasing pain intensity were significantly associated with greater impairment in functional ability (Karnofsky Performance Status, BPI functional interference index) and physical symptom distress (Memorial Symptom Assessment Scale). Results demonstrate high levels of pain and pain-related functional impairment among patients with AIDS. The presence and intensity of pain are associated with more advanced HIV disease and pain intensity is also associated with demographic factors (gender, race).