This prospective study was performed to determine the efficacy, safety, and tolerability of concurrent chemoradiotherapy (CCRT) followed by adjuvant chemotherapy with temozolomide (TMZ) in the treatment of patients with WHO grade III gliomas. Thirty-three adult patients with WHO grade III glioma and aged >17 years were enrolled from three institutions between 2003 and 2008. The median age was 41 years (range, 17-60 years). The pathological diagnoses were anaplastic astrocytomas in 21 patients and anaplastic oligodendrogliomas in 12 patients. The preoperative Karnofsky performance scale score was >60 for all patients. The patients received fractionated focal irradiation in daily fractions of 2 Gy administered five days per week for six weeks, for a total of 60 Gy, in combination with continuous daily TMZ, followed by six cycles of adjuvant TMZ. The median dose of radiotherapy was 59.4 Gy (range, 28.8-61.2 Gy) and the duration of CCRT was 7.0 weeks (range, 3.1-8.3 weeks). A median of 6.2 cycles (range, 2-12 cycles) of TMZ chemotherapy were performed during the period of adjuvant chemotherapy. The response rate was 61% and the tumor-control rate was 82%. Mean progression-free survival (PFS) was 48.7 months (95% CI, 36.0-61.4) and the 12, 24, and 36-month PFS was 74%, 60%, and 50%, respectively. Mean overall survival (OS) was 66.4 months (95% CI, 56.4-76.4) and the 12 and 24-month OS was 97% and 77%, respectively. The extent of surgical resection was a significant prognostic factor for PFS and OS (hazard ratio, 0.24; 95% CI, 0.02-0.73; and hazard ratio, 0.12; 95% CI, 0.01-0.88, respectively; P < 0.001). However, there was no significant difference in the PFS and OS of patients regarding loss of heterozygosity in chromosomes 1p and 19q and methylation of O (6)-methylguanine-DNA methyltransferase promoter, because of the small number of patients available. Only five cases (15%) receiving CCRT with TMZ and three cases (9%) receiving adjuvant chemotherapy had hematological toxicity greater than grade 3. All these patients, however, tolerated the therapy well enough to continue treatment. No opportunistic infections were noted. This protocol for WHO grade III gliomas was relatively safe and tolerable. It showed the possibility of achieving favorable results compared with those of historical controls. A randomized controlled study with a long-term follow-up may be mandatory to evaluate its efficacy.