In the period 1956 through 1981, 129 cerebrospinal fluid (CSF) shunt operations were performed on 50 patients who were residents of Olmsted County, Minn. The overall average annual age- and sex-adjusted incidence of initial CSF shunts during this 26-year period was 2.3 per 100,000 person-years. Within 5-year calendar time intervals, the average annual incidence rates per 100,000 person-years ranged from 0.8 (1956-1960) to 4.6 (1971-1975). There were 4 shunt-related deaths, 1 due to a CSF shunt infection and 3 due to acute increases in intracranial pressure. In this analysis of shunt procedures in a defined population, the diagnostic indications and changes over time in CSF shunting devices are also described.