Transient leukaemia (TL) in neonates with Down syndrome (DS) is characterized by the transient appearance of blast cells in the peripheral blood that resolves spontaneously. Some TL patients die at an early age due to organ failure. Seventy DS patients with TL were studied retrospectively to identify clinical and laboratory characteristics associated with early death (<6 months of age). Sixteen of 70 patients (22.9%) died early. The main causes of death were organ failure, particularly hepatic and cardiopulmonary failure. On univariate analysis, early gestational age (EGA), high white blood cell (WBC) count (> or =100 x 10(9)/l), percentage of peripheral blasts, elevated aspartate transaminase (AST), elevated direct bilirubin (DB), and low Apgar score were significantly associated with poor survival. On multivariate analysis, EGA, WBC count, and DB were independent predictors of poor outcome. A simple risk stratification system combining EGA and WBC count was devised to predict poor outcome. Term infants (EGA > or = 37 weeks) whose WBC count was lower than 100 x 10(9)/l had the best outcome [7.7% (3/39) died early], while preterm infants (EGA < 37 weeks) whose WBC count was higher than 100 x 10(9)/l had the worst outcome [54.5% (6/11) died early]. This stratification system may be useful for identifying high-risk patients who need early therapeutic interventions.