This article describes the secondary syringe exchange (SSE) practices of injection drug users (IDUs) attending 23 syringe exchange programs (SEPs) in the state of California during 2002 (n = 539). The sample was primarily heroin injecting, about two thirds male, half White and half other racial/ethnic groups. Participants were interviewed with a structured questionnaire that included items on sociodemographic factors, drug use practices, sexual practices, use of SEP and other social services, and satisfaction with SEP services. Interviews lasted about 30 minutes. SSE was highly prevalent: 75% of IDUs reported participating in SSE in the 6 months before interview. Program characteristics, such as legal status, SSE policy, and exchange policy, did not affect the prevalence of SSE among SEP clients. Infectious disease risk behaviors were significantly more common among SSE participants than nonparticipants. SSE participants were more likely to share syringes (p <. 001) and cookers (p <. 001) in the previous 6 months. SSE was significantly associated with being stuck with another person's syringe (needle-stick), a little-discussed “occupational hazard” of this practice. In multivariate analysis, the adjusted odds ratio of needle-stick among SSE participants was 2.8 (95% confidence interval, 1.3, 6.0). The high prevalence of SSE and the infectious disease risk associated with it warrant additional research to determine the causality of these associations. In the interim, SEPs should consider reinforcing HIV prevention education messages and training IDUs who engage in SSE in safe handling of biohazardous materials.