Some attempts have been made to reduce the costs incurred in the therapy of leukaemia, but no studies are available regarding costs of the entire treatment in children with acute lymphocytic leukaemia (ALL). We analysed all the direct costs of treatment of 11 children with ALL diagnosed and treated in Kuopio University Hospital. The follow-up continued from diagnosis until the end of treatment for each patient. Patient treatment on the ward lasted for 84-210 d and in the outpatient clinic for 24-66 d, depending on the risk group. From 11-54 of the inpatient days were required for the treatment of infections. Total mean cost of the entire treatment was US $103250 (US $55196-166039) per patient, 53% of which were basic hospital costs and 47% patient-specific costs. Laboratory tests and radiology accounted for 18% of all direct costs and cytostatic drugs for 13%, but blood products accounted for only 4% of the total. Infections were the most important extra cause of costs, accounting for 18% of the mean total costs per patient. The complete treatment of a child with ALL came to a total of US $103250. However, since 80% of children with ALL are long-term survivors, the cost must be regarded as a good investment.