Malignant non-Hodgkin's lymphomas (MHNL) in children differ from those in adults in their histological, cytogenetic and molecular biological classification and localization. LMNH is a hematological malignancy of the lymphoid tissue, constituted by a proliferation of B or T cells. It is histologically diffuse, of high grade malignancy and very rapid growth, making it a genuine medical emergency. It accounts for 10% of all pediatric cancers. This book is a guide for paediatric residents, paediatricians and paediatric oncologists. Its aim is to describe the clinical, biological and radiological aspects of childhood LMNH.