The New York City injection drug user acquired immunodeficiency syndrome (IDU AIDS) epidemic accounts for almost one quarter of AIDS cases in IDUs in the United States. Recent studies have reported declines in seroprevalence and risk behaviors among IDUs in New York City during the 1990s. These trends, however, are based on studies primarily conducted in the city's central borough of Manhattan. This article analyzes data from all five boroughs of New York City to examine trends over phases of the epidemic and to determine the level of prevention services available; an exploratory qualitative study was also conducted to assess access to prevention services and injection practices in areas in the "outer boroughs." Findings indicated that (1) borough differences in services and behaviors existed from early in the epidemic; (2) services have been concentrated in Manhattan; and (3) declines in seroprevalence were greatest among Manhattan-recruited IDUs. Enhancing access to services for IDUs in the boroughs outside Manhattan may be needed to continue the positive trends in all areas of New York City.