A total of 1,318 patients first treated for esophageal achalasia from 1935 to 1967 at the Mayo Clinic were observed an average of 13 years per patient. Carcinoma developed in seven of these patients, an incidence of 41 cases per year per 100,000. An additional six patients with achalasia and carcinoma of the esophagus had their initial treatment for achalasia either before 1935 or elsewhere than the Mayo Clinic. Achalasia had been present an average of 28 years prior to the diagnosis of carcinoma. The appearance of symptoms suggesting the possibility of esophageal malignancy occurred from two weeks to four years prior to diagnosis. Malignant tumors arose at all levels of the esophagus, and the majority were squamous cell carcinomas. Although surgical exploration was carried out in seven instances, there was only one survivor without evidence of tumor.