The objective of this study is to investigate the frequency, magnitude, and nature of peripheral nerve dysfunction in patients with cystic fibrosis (CF). Consecutive CF patients above the age of 3 years were recruited from the pediatric gastroenterology clinic. Twenty-five patients, 14 boys and 11 girls, were included, with mean age of 10.7 +/- 5.6 years. Nerve conduction studies were performed on the peroneal and median motor nerves, and median, ulnar and sural sensory nerves on one side. Fourteen patients (56%), 9 boys and 5 girls, had abnormal findings. All abnormalities were in the sensory nerves. Ulnar sensory nerve was abnormal in 48% of patients, sural sensory nerve in 44% of patients, and median sensory nerve in 28% of patients. Amplitudes were affected in all abnormal studies, associated with prolonged latencies in 20% of sural responses, 8% of ulnar responses, and 4% of median responses. Ten patients (40%) fulfilled the minimum case definition criterion for electrodiagnostic confirmation of distal polyneuropathy. Concordant abnormalities in three nerves were found in five patients (20%). The presence of neuropathy was not related to sex, age, type of CF symptoms, body mass index, or disease duration. In conclusion, CF is associated with peripheral nerve dysfunction, which is mostly sensory with an axonal trend. Care takers of patients with CF should be aware of the potential peripheral neurologic problems associated with the disease, especially with the improving survival of these patients.