Since the middle of the 20th century cancer registration has become part of many national programmes for cancer research and control. One of the main advantages of these national registers is their population based nature allowing even rare cancer diseases to be compared over time and places and analyses to be stratified on factors such as gender, age and stage of disease. Fortunately, cancer in children is very rare and for this minor group of cancer cases the use of national population based registers are of great importance for epidemiological research. For more than 30 years …