The presence of lung metastases in neuroblastoma often leads to doubt about the diagnosis due to rarity of disease at this site. To determine more precisely the incidence and nature of pulmonary disease in neuroblastoma the data base of the European Neuroblastoma Study Group (ENSG) was examined. Information was obtained about 35/746 stage IV patients (and 1 patient who was registered as having stage II disease) documented to have pulmonary disease at presentation. Of these 5 were registered with pleural effusions, 18 pleural infiltrations, and 13 intrapulmonary lesions. Review of these cases, however, suggested that only 9 patients (1.2%; 95% exact confidence interval 0.42-1.99%, binomial distribution) had disease consistent with secondary neuroblastoma in lung or pleura. There was no correlation with clinical features, age, sex, or other disease sites, and outcome was uniformly poor.