We report the results of a long-term comparative trial of physiotherapy by the positive expiratory pressure (PEP) technique with a PEP mask (Astra Meditec) versus conventional postural drainage and percussion (PD&P). Forty patients, ages 6 to 17 years, with Shwachman scores between 52 and 93, attending the cystic fibrosis clinic were enrolled in the study and randomly assigned to one of two groups. Group A (control) continued to perform physiotherapy by using PD&P for a 1-year period, whereas patients assigned to group B performed physiotherapy with the PEP technique for the same period. Compliance with physiotherapy was closely monitored for both groups throughout the study. Clinical status and pulmonary function (forced vital capacity [FVC], FEV1, and FEF25-75) were measured at 3-month intervals. Group B (PEP) demonstrated improved pulmonary function in all parameters as measured by change in percent predicted value for age, gender, and height. The changes in pulmonary function over the study period were: FVC, +6.57; FEV1, +5.98; and FEF25-75, +3.32. This improvement was significantly different from that of group A (PD&P) whose pulmonary function declined in all parameters (FVC, -2.17; FEV1, -2.28; FEF25-75, -0.24). The differences between treatment groups were statistically significant for the changes in FVC (p = 0.02) and FEV(1) (p = 0.04). Our results indicate that for our patients with cystic fibrosis, pulmonary physiotherapy with the PEP technique was superior to conventional physiotherapy with the PD&P technique.