In order to validate the information systems medicalization program used since 1984 at the Hôtel-Dieu hospital, Paris, the direct costs given by this program were compared with those calculated from the medical records of 10 adult patients hospitalized for diagnosis and treatment of acute myeloblastic leukaemia. The mean direct cost of an 8 to 81 days hospital stay was estimated at 75.393 +/- 41.260 French francs by the program and 84.969 +/- 52.288 FF by calculations from the records. A fairly good correlation (r2 = 0.72; P = 0.002) was found between the 2 evaluations. There was no statistically significant difference between the figures obtained by the 2 methods, except for pharmaceutical expenditures (P = 0.005) which were grossly underevaluated by the program. A better correlation could be obtained if an attribution of drugs and transfusions per patient was entered in the program.