Background-Malnutrition is a common management problem in patients with cystic fibrosis (CF). Various approaches to supplemental nutrition by both parenteral and enteral routes have been used. Aim-To analyse the eYcacy and acceptability of supplemental overnight feeding using a percutaneous endoscopic gastrostomy (PEG) in patients with CF. Patients-53 patients with CF (43 adults; age >17 years) with severe pulmonary disease. Methods-The technical success and complications of PEG insertion were documented together with changes in nutritional and pulmonary status of the cohort. Results-PEG tubes were successfully inserted in all patients, with immediate complications (respiratory depression) in two (4%) and late complications in 13 (25%). Feeding was well tolerated by 50/51 (98%) of the cohort during a mean (SEM) follow up of 14.5 (2.1) months. The adult cohort had a significant increase in weight and body mass index at six months which was maintained at 12 months. Serum albumin concentration remained stable at six months but had fallen by 12 months, although the diVerences were not statistically significant. These results were reflected in the paediatric cohort. Pulmonary function in those followed up for one year had apparently stabilised, but the number of admissions to hospital over the year before and the year after PEG did not change. Half of the cohort were accepted for heart-lung/lung transplantation, the improvement in nutritional status being a prerequisite for this. Conclusion-Supplemental PEG tube feeding is well tolerated and results in a significant improvement in nutritional status and an apparent stabilisation of pulmonary function in severely malnourished CF patients with advanced pulmonary disease. (Gut 1999;44:87-90)