Eighty two adult patients with histologically proven cerebral astrocytomas of grades I to IV received post-operative radiotherapy at Westmead Hospital between January 1980 and February 1985. The extent of surgery consisted of biopsy alone in 44%, subtotal tumour resection in 48%, and "complete" tumour removal in 8%. Seventy one patients completed a course of megavoltage irradiation, the majority having received a tumour dose of at least 60 Gy. Patients who underwent surgical resection (complete or incomplete) had a greater median survival (14 months) than those undergoing biopsy (8 months), but the difference was not statistically significant (p = 0.08). By grade, the difference reached statistical significance only for grade III tumours (p = 0.015). Patients with high grade tumours had a significantly lower survival than those patients with tumours of low grade. Median survival for patients with grades I and II, III and IV tumours was 42.0, 12.0 and 7.0 months, respectively. After adjustment for grade, various dosage levels (less than 60, 60 or greater than 60 Gy) did not significantly affect survival, although there was a trend towards improved median survival with higher doses in grade III tumours. Older patients (greater than 45 years) had a significantly lower median survival (25 months) than younger patients (8 months) (p less than 0.0001). When included in a multivariate analysis, the extent of surgery did not significantly influence survival, but increasing tumour grade and increasing age were significant adverse prognostic factors.