A retrospective analysis of 14 pediatric cases with fibrosing alveolitis, proved by lung biopsy, was carried out. The children were initially 6-16 years old (mean: 9.8 years) and were observed for 2 to 7 years. Symptoms had been present prior to diagnosis for 1 to 156 weeks (median: 11 weeks). The most prominent clinical findings were dyspnoea (100%), dry cough (91%), tachypnoea (85%), and weight loss (70%). Open (n = 9) or transbronchial (n = 5) lung biopsy specimens had predominantly cellular appearances in 8 children (group A) and showed predominantly fibrotic changes in 6 cases (group B). Lung function tests revealed a marked ventilatory impairment in all children. Mean vital capacity was 44% (SD 16%), and total lung capacity 58% (SD 14%) of the predicted normal values. Specific lung compliance was significantly lower in children with fibrotic changes (mean: 0.016 vs. 0.030 ml/cmH2O/ml in patients of group A, p less than 0.05). Results from 200 lung function measurements were evaluated during the follow-up. Corticosteroid treatment improved vital capacity in all children after 6 and 12 months of treatment to 64% and 62% of the predicted normal, respectively. Deterioration of pulmonary function was observed in 7 children when prednisone was tapered to below 10 mg per day. Only 4 children had a normal vital capacity at their last visit to the clinic. We conclude that children with fibrosing alveolitis experience severe alterations in lung function, and that the overall outlook is quite unfavorable.