We studied the relationship between social class and prognosis in children with acute lymphoblastic leukaemia. Seventy children who were commencing on curative therapy, and who received central nervous system prophylaxis, were included in the study. Children from social classes 1 to 5 had a significantly better five-year survival rate and duration of first remission than children from social classes 6 and 7. There was no apparent difference either in the treatment given to the two groups or in the clinical and haematological parameters studied. A study of the causes of this difference in survival could lead to better over-all results in the treatment of childhood leukaemia.