Primary lung tumours in childhood are rare. However, cancer in a child may have an impact on the lung in a number of ways. Chemotherapy and radiotherapy may be directly toxic to the lung. Young children are particularly sensitive to the effects of radiotherapy, which can cause impairment of growth of muscle, skin and bone, in addition to its direct toxic effect on the underlying lung. The lung is vulnerable to infection - particularly protozoal, viral and fungal organisms, as well as bacterial. Children undergoing bone marrow transplantation are at greater risk of lung damage, as they are profoundly immunosuppressed and have received intensive cytotoxic chemotherapy or radiotherapy. The underlying cause of lung damage may be difficult to determine because of the complexity of treatment and the additional risk of infectious complications. In a small number of children, pulmonary complications may be fatal. However, for the many survivors, although abnormalities of lung function are frequently detected, these are rarely clinically significant and, with notable exceptions, do not appear to deteriorate with time. However, data remain scanty; there is a real need for ongoing prospective studies of lung function in survivors of childhood cancer.