The records of all 96 children below the age of 15 years diagnosed with acute lymphoblastic leukaemia at Tygerberg Hospital in the Republic of South Africa between 1983 and 1995 were reviewed to determine risk factors which may predict poor outcome. Age < 2 and > 8 years, and white cell count > 20 x 10(9)/l at diagnosis were significant predictors of poor outcome. Sex, FAB classification, immunophenotype, hepatomegaly, splenomegaly, BFM risk score, and the presence of mediastinal glands did not predict outcome. The presence of the established risk factors could not adequately explain the difference in 5-year event-free survival in the three ethnic groups which was 67 per cent in white, 17 per cent in black, and 38 per cent in children of mixed ethnic origin. In an attempt to improve survival in black children, our stratification of risk groups will in future be based on factors that include ethnicity, age and WCC > or = 20 x 10(9)/l at diagnosis. Pediatric oncology services in developing countries should adapt therapy to the risk factors of their local populations.