Because HIV-infected injection drug users (IDUs) can transmit HIV infection, we investigated factors associated with sharing of syringes in the past year among IDUs infected with HIV. We analyzed data from an interview survey of 11,757 persons > or = 18 years of age with HIV or AIDS between June 1990 and August 1995 who were reported to 12 state or city health departments in the United States. Of the 1527 persons who had ever shared syringes and reported injecting in the 5 years before the interview, 786 (51%) had injected in the year before interview, and of these, 391 (50%) had shared during that year. IDUs who were aware of their HIV infection for >1 year were less likely to share (43%) than those who were aware of their infection for 1 year or less (65%, adjusted odds ratio=2.15, 95% confidence interval, 1.52-3.03). The only statistically significant time trend was that the proportion of IDUs from Connecticut who shared decreased from 71% in 1992 to 29% in 1995. This trend appears to be related to the 1992 changes in Connecticut laws that allowed purchase and possession of syringes without a prescription. Because many HIV-infected IDUs continue to inject and share, prevention efforts should be aimed at HIV-infected IDUs to prevent transmission of HIV. Early HIV diagnosis and access to sterile syringes may be important methods for reducing syringe sharing by HIV-infected IDUs.