The interval from the onset of symptoms to the diagnosis in 79 children with primary brain tumors was compared with that in 45 children with Wilms' tumor and 123 children with acute leukemia. The patients with brain tumors had a significant delay from symptom onset to diagnosis. Only 38% of primary brain tumors were diagnosed within the first month after the onset of symptoms. In contrast, 84% of Wilms' tumors and 80% of cases of acute leukemia were diagnosed within one month of the onset of symptoms. Early detection of brain tumors is important as it may have a significant bearing on clinical outcome.