Absfract. The change in radiological features of leukaemia, treated with modern methods, were studied in a retrospective investigation. Of 108 patients with leukaemia treated between 1964 and 1974 at the Children's Hospital, Heidelberg, 89 were studied. Radiological findings were divided into three groups: (i) alterations due to acute leukaemia in the initial phase (ii) late manifestations of leukaemia and (iii) alterations due to side-effects of antileukaemic therapy.It became apparent that, with prolonged survival, there was an increase in the late manifestations of leukaemia, especially in the central nervous system. This was followed by a decrease after the introduction of the therapeutic regime described by Pinkel. The immunosuppressive effect of this antileukaemic therapy gave rise to life-threatening infections, notably with Pneumocystis carinii. Besides the leukaemic manifestations in bones, kidney, and the viscera of the thorax, there were steroid-induced osteoporosis, platyspondyly and aseptic bone necrosis, and, inflammatory gastrointestinal lesions. In addition, ileus sometimes followed administration of vincristine and toxic-allergic pneumonia after methotrexate therapy occurred.