We previously reported the establishment of a rare xenograft derived from a recurrent oligodendroglioma with 1p/19q codeletion. Here, we analyzed in detail the exome sequencing datasets from the recurrent oligodendroglioma (WHO grade III, recurrent O) and the first-generation xenograft (xenograft). Somatic SNVs and small InDels ( = 80) with potential effects at the protein level in recurrent O included variants in (NM_005896:c.395G>A; p. Arg132His), (NM_003902:c.1307_1310delTAGA; p.Ile436fs), and (NM_015125:c.4421T>G; p.Val1474Gly). All but 2 of these 80 variants were also present in xenograft, along with 7 new variants. Deep sequencing of the 87 SNVs and InDels in the original tumor (WHO grade III, primary O) and in a second-generation xenograft (xenograft) revealed that only 11 variants, including (NM_005896:c.395G>A; p. Arg132His), (NM_006742.2:c.650G>A; p.Arg217Gln), and (NM_001256188:c.470G>A; p.Arg157His), along with a variant in the promoter (C250T, NM_198253.2: c.-146G>A), were already present in primary O. Allele frequencies of the 11 variants were calculated to assess their potential as putative driver genes. A missense change in (NM_022569:c.2392C>G; p.Leu798Val) on 4q exhibited an increasing allele frequency (~ 20%, primary O, 80%, recurrent O and 100%, xenograft), consistent with a selection event. Sequencing of in a cohort of 15 oligodendrogliomas, however, revealed no additional cases with potential protein disrupting variants. Our analysis illuminated a tumor evolutionary series of events, which included 1p/19q codeletion, R132H, and C250T as early events, followed by loss of function of and mutations in and as late events.