It has been suggested that criminal justice involvement among the homeless, particularly those with mental illness, is largely situational. The objective of this study was to assess, in a sample of homeless seriously mentally ill people, the prevalence of childhood conduct disorder behaviors as a risk factor for adult criminal activity as well as the extent and types of adult criminal justice contact. Data were taken from the national ACCESS program, which conducted extensive baseline interviews with 7,222 homeless seriously mentally ill adults. The interview assessed demographics, childhood risk factors for criminal activity such as conduct disorder behaviors, foster care, and parental abuse, as well as current illness severity and recent criminal justice contact. The 2-month arrest rate in this sample was much higher than national rates (11% compared with 1% annually in the general population). Although most arrests were for minor crimes (10.8%), there were also substantial rates of arrest for major (2.7%) and substance-related charges (2.0%). The prevalence of a history of conduct disorder behavior was also substantial (55% in male subjects, 40% in female subjects), and conduct disorder was a strong predictor of recent criminal justice involvement, even after controlling for other predictors of arrest (odds ratio = 1.76 for major crimes, 1.49 for minor crimes, and 1.98 for substance-related crimes). Recent literature has criticized a trend to criminalize homeless mentally ill persons for attempting to get needed food, shelter, or medical attention. However, these data indicate that at least some proportion of arrests in this population are of people who have been exhibiting antisocial behavior since early adolescence, and that early antisocial behavior is a strong predictor of all types of recent arrests in this population.