In this retrospective study the hospital records of all patients being operated on for chronic subdural haematomas (CSD) at the Neurosurgical clinic in Lund in the years 1969, 1979, 1989, and 1993 were examined. 218 patients were operated on, 25 of whom had bilateral haematomas. During the 25-year period the incidence of surgically treated CSD rose from 2 to 5.3 per 100,000 inhabitants per year. The mean age (70.5 years) and the relationship males: females (2:1) did not significantly change. The clinical condition of the patients on admission steadily improved during the period. The relative proportion of patients with known chronic alcoholism decreased over the years, but the proportion of patients suffering from other complicating diseases increased, as did the proportion of patients treated with anticoagulants. There was no mortality directly related to surgery, but if defined as deaths within one month after surgery, the overall mortality rate was 3.2%. 84.2% of the patients improved following the first operation, in a majority of cases back to the premorbid state. The relative frequency of re-operations for CSD was 12.3% and did not significantly change during the period. No pre- or peri-operative variable could be identified which could predict who of the patients was at higher risk of re-operation. Surprisingly, the data suggest that the less experienced neurosurgeons had better operative results compared with their older collegues.