Previous research finds that self-control is positively associated with adaptive and negatively associated with maladaptive behavior. However, most previous studies use cross-sectional designs, low-risk samples, and limited assessments of self-control. This study of 553 jail inmates examined the relationship of a valid measure of self-control (Brief Self-Control Scale) completed on incarceration with behavior before, during, and 1 year after incarceration. After controlling for positive impression management (PIM), self-control was negatively related to substance misuse, suicidality, risky sex, and criminal history prior to incarceration and post-release illegal substance misuse, recidivism, and positive adjustment. Lower self-control predicted increases in substance dependence at post-release compared with pre-incarceration. Self-control was not related to misbehavior during incarceration, nor alcohol use or HIV-risk behavior 1 year post-release. Results were consistent as a function of age, race, and gender. This study supports self-control as an important risk and protective factor in a sample of criminal offenders.