Lag time (the interval between symptom onset and diagnosis) was described for 2665 children with lymphoma or a solid tumor who participated in Pediatric Oncology Group therapeutic protocols from 1982 until 1988. Median lag time ranged from 21 days for neuroblastoma to 72 days for Ewing sarcoma. Significant differences in lag time were found among diagnostic groups (p less than 0.001), even after adjustment for age, gender, and race. Age was significantly associated with lag time for all diagnoses (p less than 0.05) except Hodgkin disease. Girls had increased lag times for non-Hodgkin lymphoma (p = 0.02) but decreased lag times for Ewing sarcoma (p = 0.02). Differences in lag time related to race were significant only for children with osteosarcoma (p = 0.02), for which white children had longer lag times. Type of tumor and age were strongly associated with lag time. Within diagnostic groups, age, gender, and race failed to explain more than 16% of the variance in lag time, suggesting that other factors may play more prominent roles. Further study is necessary to identify these factors and to assess the relationship between lag time, stage of disease at diagnosis, and prognosis, especially before designing early-detection interventions for childhood cancer.