One hundred and eighty-six patients with intracranial meningiomas were treated at the Royal Marsden Hospital between 1963 and 1983 with megavoltage photon irradiation (60Co gamma rays and 6-8 Mv. X rays). Survival parameters were measured from the time of referral for radiotherapy. The 10-year actuarial cause-specific survival was 67% for all cases and the actuarial disease-free survival was 61%. Both malignant and also "aggressive benign" histologies were associated with poor long-term survival. Benign angioblastic meningioma was associated with lower actuarial cause specific and disease-free survival compared with other benign histological sub-groups. Prognosis was related to the extent of initial surgical resection. Of those who underwent subtotal or partial tumor resection with post-operative radiotherapy the 10-year actuarial cause-specific survival was 77%, and in inoperable patients treated by radiotherapy alone it was 46%. Radiotherapy alone resulted in improvement of neurological performance (Karnofsky) in 12 out of the 32 (38%) patients with inoperable disease. The 10-year survival of patients referred for irradiation following "complete" surgical resection was only 34% owing to the high incidence of adverse histological sub-types in this treatment sub-group. Based upon univariate analysis, performance status of less than 60 (Karnofsky) and also age greater than 50 years at the time of referral for radiotherapy were adverse prognostic factors. Multivariate analysis revealed that histological type, extent of surgical resection and performance status at the time of presentation for radiotherapy were independent prognostic variables. However age at the time of referral lost significance as an independent variable when analyzed using this method. Patients undergoing complete surgical resection for the typical benign non-aggressive meningioma do not require adjuvant irradiation. The results of this study support the role of radiotherapy for treatment of incompletely resected and inoperable meningioma of all 3 histological types (benign, "aggressive benign", malignant).