Families are found to play an important role in adolescent substance abuse. This study examined family variables that may influence adolescent substance use during the 6 months following inpatient treatment: (1) parental substance use; (2) family aftercare attendance; and, (3) adolescent ratings of family helpfulness. It was hypothesized that the effects of parental substance use on adolescent use would be mediated by family aftercare attendance and family helpfulness ratings. Adolescent inpatients (N = 103; Mage = 16) were assessed during treatment and 6 months later. Results revealed no relationship between either parental substance use and family aftercare attendance or reports of family helpfulness. More frequent family aftercare attendance and higher ratings of helpfulness were associated with less adolescent use during follow-up. Findings highlight the importance of family behaviors on adolescent substance abuse treatment outcome.