To evaluate long-term efficacy and side effects after pneumatic dilation with low-compliance balloons, 40 patients with achalasia were prospectively studied during a 5-year period. All patients were investigated before, 4-6 weeks after, and at 28 +/- 15 months (final visit) after pneumatic dilation. Additionally, 12 patients underwent 24-hour esophageal pH-metry before and 26 +/- 14 months after dilation. Initial symptomatic success was obtained in 35 of 40 patients (87.5%). The remaining five and another seven patients with recurrent dysphagia underwent a second dilation, and two of these patients finally underwent esophagomyotomy. Effective dilation was reflected by a significant decrease of the symptom scores (p < 0.01) and an increase of the gastric cardia diameter both at 4-6 weeks after dilation and at the final visit (p < 0.01). Dilation reduced the lower esophageal sphincter pressure from 28.3 +/- 0.8 mmHg to 16.4 +/- 6.4 mmHg at the 4-6 weeks exam and to 14.7 +/- 5.5 mmHg at the final visit, respectively (p < 0.01). Neither the diameter of the esophageal body nor the motility of the tubular esophagus was affected by pneumatic. Esophageal pH-metry showed an increase of the number and duration of reflux episodes (pH < 4) after dilation (p < 0.05), whereas only one patient reported heartburn and another asymptomatic patient revealed esophagitis I0 at endoscopy. Therefore, pneumatic dilation with low compliance balloons proved to be safe and long lasting treatment of achalasia. Although prolonged esophageal acid exposure was measurable after dilation, clinically relevant gastroesophageal reflux occurred in only 5% (n = 2).