BACKGROUND: To increase access to cognitive behavioural therapy for bulimia nervosa new delivery modes are being examined. Guided Self-Help (GSH) in primary care is potentially valuable in this respect. This research aimed to compare outcomes following GSH delivered by general practitioners (GPs) in the normal course of their practice to a delayed treatment control (DTC) condition, and to examine the maintenance of treatment gains at 3 and 6 months following completion of GSH. METHOD: Participants were 109 women with full syndrome or sub-threshold bulimia nervosa, randomly allocated to GSH ( n = 54) and DTC ( n = 55). The GSH group received direction and support from a GP over a 17-week period while working through the manual in Bulimia Nervosa and Binge-Eating: A Guide to Recovery by P. J. Cooper (1995). GSH and DTC groups were assessed pre-treatment and 1 week following the 17-week intervention or waiting interval. The GSH group was reassessed at 3- and 6-month follow-up. RESULTS: Intention-to-treat analyses at end of treatment revealed significant improvements in bulimic and psychological symptoms in GSH compared with DTC, reduction in mean frequency of binge-eating episodes by 60% in GSH and 6% in DTC, and remission from all binge-eating and compensatory behaviours in 28% of the GSH and 11% of the DTC sample. Treatment gains were maintained at 3- and 6-month follow-up. CONCLUSION: Outcomes in GSH compare favourably with those of specialist-delivered psychological treatments. These findings are considered in light of the nature of the therapy offered and the primary care context.