The field of pediatric oncology encompasses four groups of malignancies - acute leukemias, brain tumors, lymphomas and solid tumors. 1'he history, diagnosis and management of children with acute leukemias and lymphomas has been thoroughly examined in several excellent textbooks of pediatric hematology and oncology. Bl"ain tumors have historically been managed by neurosurgeons and radiation therapists. 1'he role of the pediatric oncologist in the management of these patients is evolving. This book was written to provide a thorough historical evaluation of the most frequent solid tumors of children. A detailed examination of the natural history of these tumors is essential to the design and evaluation of therapeutic trials. The highly lethal nature of many of these tumors, the occurrence of some of them at several different primary sites and the rarity of these tumors have made systematic study of them difficult. Conclusions regarding the efficacy of a particular modification of the therapeutic strategy can be strongly influenced by the assumed natural history of the tumor. I have tried to develop as accurateJy as the literature would allow a picture of the natural history of the common malignant solid tumors, knowing that the image would be imperfect. I adopted a convention which was employed in all graphs constructeil from case reports summarized from the literature.