OBJECTIVES: This study examined the relationship between substance abuse patients' length of stay in community residential facilities and their outpatient mental health aftercare and readmission for inpatient care. METHODS: A national sample of 1,070 substance abuse patients referred to community residential facilities after an episode of inpatient care was assessed and followed over four years. Patients were divided into three groups: those with only alcohol-related diagnoses; those with drug-related diagnoses, most of whom also had alcohol diagnoses; and those with concomitant psychiatric diagnoses. RESULTS: Patients who had longer episodes of care in residential facilities were more likely to obtain outpatient mental health aftercare and were less likely to be readmitted for additional substance abuse or psychiatric care in six-month, one-year, and four-year follow-up intervals. Readmission rates among substance abuse patients with psychiatric diagnoses were much higher than rates among patients who had only substance abuse diagnoses. Length of stay in the community residential facility and postdischarge outpatient mental health care remained significant independent predictors of lower readmission after other risk factors for readmission were considered. CONCLUSIONS: Transitional community residential care can contribute to substance abuse patients' treatment outcome; however, longer-term supportive care is needed for substance abuse patients with more severe and chronic disorders.