We performed a randomized prospective study of pneumatic dilatation comparing a 30-mm and 35-mm Microvasive balloon dilator inflated for either 15 or 60 sec in patients diagnosed with idiopathic achalasia who were previously untreated. Twenty-four patients, 11 men, 13 women, mean age 45, range 18-81 years), were prospectively randomized for dilatation. History and physical examination, esophageal manometry, and barium swallow were performed before dilatation. Symptom self scores were assessed before dilatation, and one month and six months after dilatation. Pneumatic dilatation was successfully completed in all 24 patients, with one patient experiencing a confined perforation. Conservative treatment was employed, and the patient recovered fully. Two patients experienced a recurrence of symptoms and required a second dilatation. Evaluation of posttreatment symptom self scores indicates no difference between the 30-mm and 35-mm Microvasive balloon or inflation durations of either 15 or 60 sec. These data indicate that the more conservative 30-mm dilator inflated for just 15 sec delivers a symptom response equal to a more aggressive approach with the larger dilator inflated over longer duration.