This study was designed to describe demographic and drug use characteristics, health status, and HIV-related risk behavior among clients attending the San Francisco needle exchange program (NEP), and to assess the relationship between NEP utilization and risk behavior. Randomly selected clients were interviewed when they visited the NEP. Participants were of diverse ethnicity, had a mean age of 38.2, and 72% were male. Many reported being homeless (25%), unemployed (34%), uninsured (52%), and having an episode of infectious disease in the past 2 years (36%). Clients who received a higher proportion of their needles from the exchange were less likely to report sharing of needles or rinse water. Clients who attended the exchange more frequently were more likely to clean their skin prior to injecting and less likely to use the same needle repeatedly. Frequency of visiting the NEP was not associated with the likelihood of sharing needles or rinse water. Efforts to evaluate needle exchange in the United States will benefit from descriptive reports from other NEP programs, and the use of nonexchange comparison groups.