To compare the outcome from adjuvant and delayed radiotherapy (RT) after surgery in patients with benign cerebral meningioma. Between March 1953 and January 2001, 92 patients with benign cerebral meningioma (WHO grade I) were treated with surgery. Forty-eight patients underwent gross total resection (GTR), and 44 patients underwent subtotal resection (STR). Treatments were classified as GTR ( n=48), STR+adjuvant RT ( n=12), STR alone ( n=32). The prognostic factors were assessed as, gender, the Karnofsky performance score (KPS) (≥90 vs. <90), the extent of surgery, and adjuvant or delayed RT. The endpoints analyzed were progression-free survival (PFS) and overall survival (OS). Overall survival curve of the study population is compared with the age-adjusted expected survival curve for the US population born in 1970. The median follow-up was 7.7 years. The 5-year PFS and OS rates for all patients were 65 and 93%, respectively. The 5-year PFS rates in patients treated with GTR and STR were 77 and 52%, respectively ( P=0.02). Patients treated with STR+adjuvant RT had significantly better PFS (91%) at 5 years than with STR alone (38%) ( P=0.0005). Gender showed no statistically significant impact on either PFS or OS ( P>0.05). However, multivariate analysis showed the KPS to have a statistically significant effect on OS ( P=0.02). The OS rate was the same across all three treatment groups. The age-adjusted expected survival curve for the US population born in 1970 lay within the confidence intervals for the overall survival curve of the study population. Although OS was not affected, adjuvant RT appeared to significantly reduce tumor progression. However, only a prospective randomized trial can adequately determine whether adjuvant or delayed radiotherapy is the better approach in patients with subtotally resected benign meningioma.