A cross-sectional design was used with 294 patients interviewed between January 1996 and October 1997. Patients came from 15 settings that offered treatment, counseling, or assistance to drug users of HIV-positive patients in Sao Paulo, Brazil. The structured interview schedule developed and administered to the subjects consisted of 246 questions that covered sociodemographic details, drug history, cocaine transitions, and HIV-risk behaviors. Findings show that 87 percent of the patients began using cocaine by snorting it; and 74 percent subsequently underwent a transition of route, with 68 percent smoking cocaine and 20 percent injecting it. Half of all these transitions occurred in the first 3 years following initiation into cocaine use. Factors associated with transitions were younger age at cocaine initiation, more frequent use at peak usage, initial use of cocaine by snorting or injecting, a lower level of scholastic attainment, and experience with a wider range of drug classes. A cohort effect was apparent with younger cocaine users, and those who had begun using after 1990 were more likely to undergo a transition to smoking crack; they were less likely to start injecting. The study concludes that cocaine transitions are common and are usually toward routes associated with a higher dependency potential and increased HIV-risk behavior. Further research is needed to determine whether transitions can be prevented by early identification of potential cases. 5 tables, 1 figure, and 21 references