The effect of pneumatic dilation and Heller esophagomyotomy on esophageal diameter was studied in 49 patients with achalasia. Standardized radiologic technic was used with the patient in a horizontal position and with a 36-in. target-to-film distance. Fifteen normal subjects had a mean esophageal diameter (± SD) of 1.50±0.37 cm, while that in untreated patients was 4.85±1.44 cm. When pneumatic dilation resulted in a fall in mean diameter to 2.27±0.49 cm, symptoms improved; they persisted in those with a diameter of 4.99±1.23 cm. Heller esophagomyotomy led to a decrease in diameter to 2.29±0.62 cm in those with relief of symptoms, while symptoms continued in those with a diameter of 4.35±0.80 cm. In a longitudinal study of individual patients, it was noted that when treatment resulted in a diameter of less than 3.0 cm, symptoms improved. If esophageal size remained over 3.0 cm after treatment, however, dysphagia or pain recurred and persisted. Serial measurements of esophageal diameter, therefore, may be valuable in the clinical management of achalasia.