Improved survival of pediatric cancer patients will lead to an increase of late sequellae such as secondary malignant neoplasms (SMN). Specific pediatric factors predisposing to these SMN are as follows: long expecting duration of life, high cellular proliferative potential, toxicity of often combined cancer therapies (radio- and chemotherapies) and more frequent genetic predisposition to cancer. Better understanding of these factors could improve patients management and could lead to the development of less toxic future therapies with the hope to decrease the risk of SMN.