AIMS Cognitive-behavioral therapy (CBT) is useful for treating substance abusers, and recent data suggest it is also efficacious for pathological gamblers. CBT is purported to exert its beneficial effects by altering coping skills, but data supporting coping changes as the mechanism of action are mixed. This study examined whether coping skills acquisition mediated the effects of CBT on decreasing gambling in pathological gamblers. DESIGN Participants were assigned randomly to CBT plus referral to Gamblers Anonymous (GA) or to GA referral alone. SETTING Out-patient clinic. PARTICIPANTS A total of 127 pathological gamblers. MEASUREMENTS Participants completed the Coping Strategies Scale (CSS) before treatment and 2 months later; indices of gambling behavior and problems were administered pretreatment and at months 2 and 12. FINDINGS Overall, CSS scores increased for participants in both conditions, but those receiving CBT evidenced larger increases than those in the GA condition (P < 0.05), and they also reduced gambling more substantially between pretreatment and month 2. Changes in CSS scores mediated the relationship between treatment assignment and gambling outcomes from pretreatment to month 2, but little evidence of mediation occurred for the long-term follow-ups. CONCLUSIONS CBT's beneficial effects in decreasing gambling may be related partly to changes in coping responses, and improvements in coping are associated with long-term changes in gambling. However, relationships between coping skills and gambling behavior are fairly strong, regardless of treatment received.