Within a statewide random sample of 611 young adult patients who received public inpatient, outpatient, and community residential care, 38 percent were found to have been arrested at least once in their adult lifetimes. Thirty-five percent had been arrested for felonies and 18.9 percent for violent crimes. Analyses by five major diagnostic groups showed that patients with a primary diagnosis of drug or alcohol abuse had the greatest overall frequency of arrests and also the greatest frequency of arrests for burglary, offenses against public order such as peace disturbance or loitering, and probation and parole violations. No significant differences between diagnostic groups were found for arrests for violent crimes. Characteristics that predicted which patients would be arrested in the year after receiving mental health services were a greater number of lifetime felony arrests, younger age, being black or a member of another minority group, and more years since first receiving public mental health care.