Since 1976 the Swiss Paediatric Oncology Groups (SPOG) has registered leukaemia cases occurring in Switzerland. The registration was set up for clinical research; however, since 1985 efforts have been made to complete the registers with cases not taking part in a clinical trial. The data of the SPOG register between 1976 and 1989 are compared to data from cancer registers and the mortality statistics of the Federal Office of Statistics. Between 1985 and 1988 the SPOG register included 91% of the cases recorded by the six cantonal registries. Compared to mortality data, registration was 100% in 1989. The SPOG data file can therefore be assumed to be complete enough to be used for epidemiological studies on incidence of leukaemias and on time trends of leukaemias in Switzerland.