To determine the course of esophageal hiatal hernia not surgically treated, we investigated the status in 1959 of 365 cases diagnosed but not corrected at the Mayo Clinic in 1949. Of 301 patients with sliding esophageal hiatal hernias, approximately 60 per cent were asymptomatic or improved after 10 years, regardless of the size of the hernia, whereas of 58 patients with the short-esophagus type of hernia, the asymptomatic or improved were only about 40 per cent. Among the group with sliding hernia, however, 82 per cent of those having minimal symptoms were improved, but only 39 per cent of those having esophagitis. Complications affecting the prognosis included esophagitis, peptic ulcer, cholelithiasis, and age, but not duration of symptoms before diagnosis. Death and grave complications were uncommon.