The objectives of this study were to describe characteristics and utilization patterns of participants attending a needle-exchange program (NEP) in Chicago, Illinois. Since 1994, demographics of NEP attendees and program utilization data were collected systematically at 22 sites operated by the Chicago Recovery Alliance (CRA). Descriptive statistics were used to assess time trends, site variations, and characteristics of attendees in day sites versus evening sites. A total of 11,855 injection drug users (IDUs) visited the NEP at least once from 1994 to 1998. Median age was 41 years, and 74% were male. Overall race distribution was African-American 50%, Caucasian 38%, Puerto Rican 10%, other 2%. Over time, there was a proportional decrease in African-American users (55.4% to 39.9%, P < .001), a significant increase in Puerto Rican users (1.4% to 14.1%, P < .001), and a stable proportion of Caucasian users (42%). Each year, 15-20% of all clients were first-time attenders. Overall, participants attending evening versus day sites were younger (median age 39 years vs. 42 years, P < .001) and more ethnically diverse. Over a 4-year period, this NEP reached a diverse population of IDUs and recruited a stable proportion of first-time users. Compared to daytime NEP venues, evening NEP sites attracted younger clients and those who were more diverse ethnically. To maximize coverage of sterile syringes, NEPs should strive for diversification in terms of hours of operation and location.