Medulloblastoma: a population-based study of 532 cases. Five hundred thirty-two cases of medulloblastoma (males n = 327 and females n = 205), aged 0 to 86 years diagnosed between 1973 and 1986 were studied to determine the incidence in different geographic regions of the United States and to evaluate the effect of various factors on survival. The median age was 9 years and average follow-up time was 45 months. The overall incidence rate was 1.8 per one million person-years. Variables that were statistically significant (p less than 0.05) in a multivariate model determining survival in rank order were treatment group, sex, geographic region, year group and age. This observational study found that 1) age and sex were statistically significant factors in describing the incidence rates, whereas year group and geographic region were not; 2) no incidence peak in the third decade of life was observed; 3) a significant improvement in survival was observed in the combined 1978 to 1986 year groups relative to the 1973 to 1977 year group; 4) the overall 5-year survival probability was 45%; and 5) there has been an increase over time in the use of more than two modalities of treatment. 