Achalasia is an uncommon esophageal motility disorder of unknown etiology. To gain insights into possible etiologic risk factors, demographic and comorbidity data were obtained from Medicare hospital discharge data files from 1986-1989 on patients aged 65 and older. Age-adjusted sex- and race-specific occurrence rates were calculated for each US state. The rate of comorbid illness occurrence in achalasia patients was compared to that of the entire hospitalized Medicare population. Records of 15,000 achalasia discharges were available for analysis. Achalasia discharge rates increased linearly from age 65 to 94 years. They were similar in males and females as well as whites and nonwhites. High rates were observed in the South and low rates in most states of the East North Central region around the Great Lakes and in the Pacific region. The same geographic pattern was observed in men and women as well as in the two separate subsets of data representing the periods 1986-1987 and 1988-1989. Achalasia was associated with a significantly increased risk for pulmonary complications, malnutrition, and gastroesophageal cancer. The concordant occurrence of achalasia in patients with Parkinson's disease, depressive disorder, and various other myoneural disorders indicated a possible etiologic relationship. Achalasia appears to represent the clinical end point of several different pathways. Besides aging, different neurologic diseases may contribute to a loss in control of esophageal motility. The geographic pattern could suggest the influence of environmental factors.