This study aimed to evaluate the prognostic significance of co-polsomy of chromosome 1q and 19p in 1p/19q codeleted oligodendroglial tumors (ODGs). In a series of 148 ODGs with 1p/19q deletion, co-polysomy of 1q and 19p was detected by fluorescence in situ hybridization (FISH). Log-rank analysis and Cox regression methods were used to compare KaplanMeier plots and identify factors associated with worse prognosis. There were 104 (70.3) low-grade ODGs and 44 (29.7) high-grade ODGs. Co-polysomy was independently associated with shorter progression-free survival and overall survival in 1p/19q codeleted ODGs, irrespective of tumor grades. The odds ratio of without and with co-polysomy was 0.263 (95 confidence interval [CI], 0.0890.771; P .015) for progression-free survival and 0.213 (95 CI, 0.0600.756; P .017) for overall survival. Subgroup analysis confirmed this trend in both low-grade and high-grade ODGs, although the P value for high-grade ODGs was marginally significant. Co-polysomy of 1q and 19p could be used as a marker to independently predict worse prognoses and guide individual therapy in 1p/19q codeleted ODGs.