BACKGROUND/AIMS: Pneumatic dilation is the most effective non-surgical treatment option for the patients with achalasia. The aim of this study was to determine the predictors of outcome after pnematic dilation in patients with primary achalasia. METHODS: Thrity-five patients with primary achalasia between May 1996 and April 2001 were included. They were divided into two groups; responder and nonresponder. Esophageal manometry, scintigraphy and barium esophagogram was performed before dilation and 4 weeks after dilation. RESULTS: Seven patients having symptomatic relapse were treated with repeated pneumatic dilation. Remaining 28 patients (83%) had no recurrence during follow-up period (mean duration 16 month, range 6~43 month). Among the factors evaluated in the initial examination, only young age affected outcome (p=0.039). The post treatment retention fraction at 5, 20 minutes were the most valuable factors for predicting the clinical response (p<0.05). CONCLUSIONS: Older patients are more likely to have sustained response. Radionuclide esophageal emptying test remains a useful objective study evaluating esophageal transit before and after pneumatic dilation in the patients with achalasia and may have an important role in the follow-up evaluation of treatment for achalasia.