Since 1976 the Lombardy Cancer Registry (RTL) has recorded all malignant tumors and the benign tumors of the nervous system, bladder and liver occurring in the Varese province. The aims of this report are: to describe age-specific incidence rates of the different oncotypes of primary nervous system tumors (PNSTs) and to analyze the duration of survival of the patients according to the histotype of the neoplasm. From 1976 to 1981, the RTL recorded 498 PNST: 213 tumors of glial origin, 132 tumors of mesodermal tissues, 15 tumors of multipotential cell origin, 37 tumors of nerve roots, 8 of vascular origin, and 54 PNST in which the histotype was not specified. For tumors of glial origin, the 60-69 year age class showed the highest incidence rate: 16 per 100,000/year. The incidence rate of tumors of mesodermal tissues reached the maximum value of 7.9 per 100,000/year in the age group of 75 years and over. Tumors of multipotential cell origin had a maximum incidence of 2.2 in the 60-69 year age class. The probability of survival at 5 years after diagnosis was computed by the method of Kaplan and Meier, and the log rank procedure was used to test statistical differences among survivors. Tumors of glial origin, excluding ependymomas and papillomas of choroid plexus, had a 5-year survival probability of 14%. Age (categorized in less than or equal to 50 and greater than 50 years) and histologic grade (grades I + II and grades III + IV) were analyzed as prognostic factors for tumors of glial origin: a younger age was the most predictive prognostic factor in grade I + II tumors (probability of survival = 53% in the group less than or equal to 50 years vs 0 in the group greater than 50 years; p less than 0.005). In the less differentiated tumors there were no differences between the two age groups. Patients with tumors of mesodermal tissues had a 5-year probability of survival of 83%. Subjects younger than 50 years had a probability of survival of 95%, whereas older patients had a probability of 79%. For the other oncotypes, the 5-year survival probability was: 50% for tumors of multipotential cell origin, 63% for ependymomas and papillomas of the choroid plexus, 64% for tumors of vascular derivation, and 21% for PNST with not specified histotype.