In a follow-up study of 147 patients with achalasia of the esophagus treated by myotomy, 146 patients were traced (58 female and 88 male patients aged 4 to 83 years [median, 46 years]). The living persons were contacted in writing or by telephone. The mean follow-up time after the operation was 23.2 years (range, 6 to 41 years). The cause of death was established for 71 patients. There were three postoperative deaths and two deaths following recurrence. In comparison with the Danish population, the 66 remaining patients were found to have a relatively higher cancer mortality (33.8 percent). Contrary to the expected less than one, ten of 23 patients who died of cancer had a malignant tumor in the esophagus. The mortality rate after 30 years was 66.1 percent, 11.9 percent of the deaths caused by esophageal cancer. It is concluded that there is a connection between achalasia and cancer of the esophagus that ought to be considered in the treatment and follow-up of patients with achalasia.