OBJECTIVE: Increasing the availability and accessibility of evidence-based treatments for eating disorders is an important goal. This study investigated the effectiveness and cost-effectiveness of guided self-help via face-to-face meetings (fGSH) and a more scalable method, providing support via email (eGSH). METHOD: A pragmatic, randomized controlled trial was conducted at three sites. Adults with binge-eating disorders were randomized to fGSH, eGSH, or a waiting list condition, each lasting 12 weeks. The primary outcome variable for clinical effectiveness was overall severity of eating psychopathology and, for cost-effectiveness, binge-free days, with explorative analyses using symptom abstinence. Costs were estimated from both a partial societal and healthcare provider perspective. RESULTS: Sixty participants were included in each condition. Both forms of GSH were superior to the control condition in reducing eating psychopathology (IRR = -1.32 [95% CI -1.77, -0.87], p < .0001; IRR = -1.62 [95% CI -2.25, -1.00], p < .0001) and binge eating. Attrition was higher in eGSH. Probabilities that fGSH and eGSH were cost-effective compared with WL were 93% (99%) and 51% (79%), respectively, for a willingness to pay of £100 (£150) per additional binge-free day. DISCUSSION: Both forms of GSH were associated with clinical improvement and were likely to be cost-effective compared with a waiting list condition. Provision of support via email is likely to be more convenient for many patients although the risk of non-completion is greater.