This study comprises 277 primary open-angle glaucomas in 239 patients followed up to 10 years after trabeculectomy. Sixty-four per cent had capsular glaucoma and 36% simple glaucoma. The number of cases showing no progression of glaucoma damage and not needing additional medical therapy decreased slowly with time. Seventy-five per cent showed no progress after one year, 70% after 2 years, 57% after 5 years and 42% after 10 years. There was a significant trend that fewer capsular glaucomas progressed than simple glaucomas. High pressure levels before trabeculectomy did not indicate a bad prognosis. Cases with advanced or moderate glaucomatous damage seemed to have the same prognosis. Cataract was a common complication; a 50% reduction of preoperative visual acuity was found in 37% of eyes after 5 years of follow-up.