Ferritin was measured in sera obtained at diagnosis from 241 patients with neuroblastoma to determine (a) the incidence of elevated ferritin and (b) the relationship between ferritin level and outcome. Ferritin was infrequently elevated in sera from patients with Stages I and II disease but was abnormally elevated in 37 and 54% of those with Stages III and IV neuroblastoma, respectively. The mean and median levels for each stage were compared and were highest for Stages III and IV disease. Analysis of progression-free survival for children with Stages III and IV disease indicated that elevated ferritin was associated with a significantly poorer prognosis than was normal ferritin and that this correlation was independent of stage and age at diagnosis. Progression-free survival at 24 months of follow-up for patients with Stage III disease with normal ferritin was 76% and with elevated ferritin was 23%. For those with Stage IV disease, progression-free survival was 27 and 3% with normal and elevated ferritin, respectively. We conclude that determination of the level of ferritin in serum at diagnosis is useful for selecting appropriate therapy for patients with Stage III neuroblastoma. Those with normal ferritin (63% of patients) have a good outcome with current therapy, but those with elevated ferritin (37%) do poorly and require more effective therapy. Although ferritin defines subgroups with Stage IV disease, the outcome of all groups must be improved.