The study sample consisted of 727 patients (435 men and 292 women) who were participating in 21 methadone treatment programs in 11 U.S. cities from 1991 to 1993. Assessment at treatment entry found that a greater proportion of men than women abused alcohol, lived with their parents, were under legal supervision, and were employed. A greater proportion of women received public assistance, were depressed, had a substance-abusing spouse, and engaged in high-risk sexual behavior. Cocaine use was related to continued heroin use for both men and women, regardless of patterns of treatment participation. Using alcohol, living with one's parents, and having associations with a negative reference group were associated with poorer treatment outcomes among women who received methadone treatment during the follow-up period. Pressure from a criminal justice agency was associated with abstinence for men who were not in treatment. The study concluded that counselors can be an important source of support for continued treatment participation and abstinence by addressing patients' concerns about their levels of social and familial support, particularly for women who live with their parents. Future research should explore in greater depth whether therapeutic processes within methadone treatment that directly address patients' needs for social and familial support improve treatment outcomes for both men and women. 3 tables and 23 references