OBJECTIVE: To verify the role of peak expiratory flow, measured through portable meters, as an alternative test to assess pulmonary disease in cystic fibrosis. METHODS: Forty-nine patients aged five to 19 years old in stable health condition and able to perform the peak expiratory flow maneuver were included. In the same visit, Shwachman-Kulczycki score was recorded. Linear regression was used to assess the correlation between the Shwachman-Kulczycki score and the peak expiratory flow rate. A P value of 0.05 was considered to be significant. RESULTS: A slight, but statistically significant correlation between absolute and percent values for this functional parameter and the Shwachman-Kulczycki score (r = 0.31, P = 0.02 and r = 0.30, P = 0.03, respectively) was found. CONCLUSIONS: Although this correlation was statistically significant, these findings are not clinically relevant, i.e., the lung involvement in this disease should be assessed by classic pulmonary function tests, such as spirometry.