In this exploratory analysis, we assessed the effect of drug use among social-network members on recovery from drug dependence in patients with co-occurring bipolar disorder. Patients (n = 57) enrolled in a group therapy study completed assessments over 15 months. Patients with zero to one drug users in their social networks at intake had few days of drug use during treatment and follow-up, whereas those with >/= 2 drug users had significantly more days of drug use. Multivariate analysis showed that patients who consistently named multiple drug users in their social networks had a marked increase in drug use over 15 months, while those who never or occasionally named multiple drug users had a small decline in drug use over time. Multiple drug users in social networks of treatment-seeking drug-dependent patients with co-occurring bipolar disorder may indicate poor drug use outcomes; efforts to reduce the association with drug users may be useful. This clinical trial has been registered in a public trials registry at clinicaltrials.gov (identifier is NCT00227838).