Over the period from 1978 to 1984, 673 neoplastic diseases were ascertained in boys and 517 in girls below the age of 15 years in the population-based cancer registry of Slovakia, giving average annual incidence rates of 142.7 and 114.2, respectively, per million population. With the large use of a standard international classification based on cell morphology, an analysis of very detailed structure of these tumors could be performed. Leukemias, tumors of the nervous system and lymphomas were responsible for nearly 70% of all malignancies in childhood during the period studied. Important increase of the total cancer incidence in boys accompanied only by its slight growth in girls during the longer period 1968-1984 was observed. The decline of the total childhood cancer mortality in Slovakia was less rapid than that observed in recent decades in some developed countries. These findings indicate at least the real existence of opportunities for the reduction of mortality from cancer in childhood in this country, too, obviously by a more effective and general application of actually available methods of treatment.