People who inject drugs (PWID) and have mental health conditions, such as major depression, an anxiety disorder, or antisocial or borderline personality disorder, may have elevated risk for HIV and HCV infection. This study examined the associations between psychiatric disorders and risky injection behavior in an out-of-treatment sample of young PWID. We recruited participants through outreach and respondent-driven sampling (RDS). Participants completed a computer-assisted self-interview and a psychiatric interview. Interviews took place at a community-based field site of the Community Outreach Intervention Projects. Participants were 570 young adults (18 to 25 years) who injected drugs in the previous 30 days. Psychiatric diagnoses were based on interviews using the Psychiatric Research Interview for Substance and Mental Disorders (PRISM). Injection behavior was classified into 3 categories: receptive syringe sharing, other equipment sharing only, and no sharing. Associations between injection risk behavior and psychiatric diagnoses were tested using RDS-weighted multinomial regressions. Substance-induced lifetime and past-year major depression, and borderline personality disorder, were significantly associated with a greater likelihood of receptive syringe sharing (p<.001). Substance-induced major depression in the past year was also associated with nonsyringe equipment sharing (p<.01). Primary major depression, antisocial personality disorder, and anxiety disorders other than posttraumatic stress disorder were slightly more prevalent among injectors who shared syringes; however, the associations were not statistically significant. Substance-induced major depression and borderline personality disorder are common among young PWID and are associated with risky injection behavior.