Childhood tumors are classified into 12 major diagnostic groups: leukemias, lymphomas, central nervous system (CNS) tumors, sympathetic nervous system tumors, retinoblastomas, renal tumors, liver tumors, bone tumors, soft tissue sarcomas, germ cell tumors, epithelial tumors and other and unspecified malignant cancers. Epidemiological studies have shown an association between exposure to medical radiation during pregnancy and risk of childhood cancer in offspring. The effects of maternal lifestyle during pregnancy on embryonic and fetal development are well known effects on the subsequent risk of cancer. Several features of maternal lifestyle during pregnancy have been studied regarding their association with childhood cancer, including diet, breastfeeding, smoking and alcohol consumption and the use of cosmetics. Parental illicit drugs use has been associated with several types of childhood cancer. Lymphoma, melanoma and testicular, cervical and thyroid cancers account for the vast majority of cancers in adolescents and young adults.