Adolescent drug abuse clients (N = 176) and their mothers, in six different outpatient drug-free programs, were assessed at admission and at follow-up, 15 months after initiation of treatment. Family therapy sessions were offered in all six programs programs in addition to individual and group counseling. The pretreatment assessment procedures, and thus also the variables analyzed for prediction of treatment outcome, emphasized family measures (including the Family Environment Scale, the Family Adaptability and Cohesion Scale, the Parent-Adolescent Communication Inventory, and other information about the family and the parents). Multiple regression analysis determined which of three demographic variables and 39 other independent pretreatment predictor variables had a significant relationship with each of the six outcome criteria (dependent variables). Four of these outcome criteria were based on client information, and two were based on information provided by the mother. The more positively the family's functioning and relationships were described by the client at pretreatment, the more client improvement was reported by either client or mother at follow-up. Eleven of the 12 predictor variables that were found to be significantly related to any of the treatment outcome criteria were measures, at pretreatment, either of the client's perceptions of family functioning, or of his or her relationship with parents, particularly with the mother. These findings show the power of the family factors as indicators of prognosis. The predictor variable that was found to have the largest number of significant relationships, predicting three of the six outcome criteria, was the "family independence" dimension of the FES (i.e., "The extent to which family members are encouraged to be assertive, self-sufficient"). It appears that the FES instrument may be quite effective for predicting improvements in the behavior of adolescent drug-abusing clients.