Objective To compare the cost effectiveness of social behaviour and network therapy, a new treatment for alcohol problems, with that of the proved motivational enhancement therapy. Design Cost effectiveness analysis alongside a pragmatic randomised trial. Setting Seven treatment sites around Birmingham, Cardiff, and Leeds. Participants 742 clients with alcohol problems; 617 (83.2%) were interviewed at 12 months and full economic data were obtained on 608 (98.5% of 617). Main economic measures Quality adjusted life years (QALYs), costs of trial treatments, and consequences for public sector resources (health care, other alcohol treatment, social services, and criminal justice services). Results Both therapies saved about five times as much in expenditure on health, social, and criminal justice services as they cost. Neither net savings nor cost effectiveness differed significantly between the therapies, despite the average cost of social behaviour and network therapy (£221; $385; 320) being significantly more than that of motivational enhancement therapy (£129). If a QALY were worth £30 000, then the motivational therapy would have 58% chance of being more cost effective than the social therapy, and the social therapy would have 42% chance of being more cost effective than the motivational therapy. Conclusion Participants reported highly significant reductions in drinking and associated problems and costs. The novel social behaviour and network therapy did not differ significantly in cost effectiveness from the proved motivational enhancement therapy.