Recent research indicates that approximately 60% of children diagnosed with cancer in Britain are cured and as a result, about 1 in a 1000 of the general population will soon be survivors of childhood cancer. Unfortuately some elements of the therapies which are responsible for this remarkable success are associated with serious complications, sometimes decades after their administration, Therefore, a comprehensive knowledge of the risks and benefits of different therapies will only be obtained by monitoring the health of survivors indefinitely. With such therapeutic success, increasingly the composition of future treatment protocols will be influenced by knowledge of the risks of long term morbidity and mortality associated with past therapies. An awareness of the long term risks of complications of treatment is also important for estimating the future demand on the health services of this increasing proportion of the general population who together represent many life years of care. This chapter reviews what is known concerning the long term risks of complications of different treatments. Appropriate strategies for future clinical and epidemiological follow-up of the survivor population are discussed and the need for indefinite follow-up of the survivor population is emphasised.