This paper reports on an analysis of nearly 27,000 hematological malignancies diagnosed in the U.K. in the 10-year period 1984 to 1993. The unique observations provided in this analysis are the similarity of the sex-specific curves by age for acute myeloid leukemia, myelodysplasia types, polycythemia rubra vera, and myelofibrosis (or myelosclerosis). The unusual age-sex-specific distribution of essential thrombocythemia, suggesting a unique epidemiology, has never been reported before. The unusual female excess of the nodular sclerosing adolescent peak in Hodgkin's disease and its rapid fall with time is potentially of great importance. An even younger childhood peak of acute lymphoblastic leukemia is presented. Overall these data represent the most reliable available in the U.K., being population based, specially collected and will form the basis of considerable further investigations.