Although anaplastic oligodendroglial tumors are known to be chemosensitive, patients under this diagnosis have been traditionally treated with radiotherapy. To avoid possible neurotoxicity, we prospectively treated patients with anaplastic oligodendroglial tumors harboring 1p/19q deletion, with exclusive procarbazine, ACNU, and vincristine chemotherapy without radiotherapy. Twenty-five patients were enrolled in the study (12 with 1p/19q co-deletion, 2 with 1p mono-deletion, 2 with 19q mono-deletion, and 9 without 1p/19q deletion). The median progression-free survival (PFS) was 50 months for all the patients, and those with tumors harboring 1p/19q deletion were progression free for a significantly longer period than those without the deletion (p=0.0391). The median overall survival (OS) time was not reached in both patient groups with and without 1p/19q deletion (p=0.230), and the 5-year OS rate was 62.2% for all patients. The excellent treatment results warrant a large-scale clinical study to confirm the efficacy of upfront chemotherapy omitting radiotherapy as initial therapy for anaplastic oligodendroglial tumors with 1p/19q deletion.