Radiation therapy with concomitant and adjuvant temozolomide (TMZ) is the standard therapy for nonelderly patients with glioblastoma. However, TMZ-based chemoradiotherapy for elderly patients with glioblastoma is controversial. The aim of this study was to investigate the benefits and adverse effects of this combined therapy in elderly patients with glioblastoma. Of the 76 newly diagnosed glioblastoma patients who were treated with standard radiotherapy (60 Gy/30 fractions) and TMZ, treatment toxicity and therapeutic outcome were evaluated in 27 elderly patients (age 65 years or older) and compared with those of 49 nonelderly counterparts (age younger than 65 years). The incidence of common toxicity criteria Grade 4 adverse events during the concomitant course was higher in the elderly group than that in the nonelderly group (26% versus 8%; p = 0.046). Cognitive dysfunction was observed only in the elderly group (p = 0.042). The median overall survival (OS) and median progression-free survival in the elderly group were 15.2 months (95% confidence interval [CI]; 12.9-18.5) and 8.4 months (95% CI; 5.1-11.7), respectively. OS was significantly shorter in the elderly group than in the nonelderly group (p = 0.021). The recursive partitioning analysis score was a prognostic factor for OS. TMZ-based chemoradiotherapy was associated with an increased risk of Grade 4 adverse events in the elderly patients during concomitant use. Thus, elderly patients who undergo a concomitant course of TMZ must be closely monitored for adverse events. Treatment of glioblastoma in elderly patients must be optimized to reduce toxicity to acceptable levels and to maintain efficacy.