OBJECTIVE The aim of this study is to identify factors that will predict which patients with benign gastric outlet obstruction will not respond to endoscopic balloon dilation, in a long-term observation. METHODS Over a 51-month period, 42 patients with benign gastric outlet obstruction received endoscopic balloon dilation. The "through-the-scope" technique with the aid of a guide wire was used for dilation. Fifteen factors were analyzed prospectively in 40 patients. Multivariate analysis was used to find the independent factors of the failure of treatment. RESULTS The median follow-up period was 23 months (range 1-51 months). Twenty-eight (67%) patients achieved sustained improvement, and 14 (33%) patients underwent surgery. The overall symptom-free rates in 12, 24, 36, and 48 months were 85.3%, 78%, 68.8%, and 68.8%, respectively. The independent prognostic factor for failure of treatment was the need for more than two courses of endoscopic balloon dilation to relieve symptoms (odds ratio, 6.857; 95% confidence interval, 1,031-45,606). CONCLUSIONS Endoscopic balloon dilation for the treatment of benign gastric outlet obstructions is an effective alternative to surgery. Patient who needs more than two courses of endoscopic balloon dilation to relieve symptoms should receive surgery.