Pathophysiological hypoxia, which fosters the glioma stem-like cell (GSC) phenotype, is present in high-grade gliomas and has been linked to tumor development, invasiveness and resistance to chemotherapy and radiation. Oncolytic virotherapy with engineered herpes simplex virus-1 (HSV-1) is a promising therapy for glioblastoma; however, the efficacy of γ 1 34.5-deleted HSVs, which have been used in clinical trials, was diminished in hypoxia. We investigated the ability of a chimeric human cytolomegalovirus (HCMV)/HSV-1 virus, which expresses the human CMV protein kinase R evasion gene IRS1 and is in preparation for clinical trials, to infect and kill adult and pediatric patient-derived glioblastoma xenografts in hypoxia and normoxia. Infectivity, cytotoxicity and viral recovery were significantly greater with the chimeric virus compared with the γ 1 34.5-deleted virus, regardless of oxygen tension. The chimeric virus infected and killed CD133+ GSCs similarly to wild-type HSV-1. Increased activation of mitogen-activated protein kinase p38 and its substrate heat-shock protein 27 (Hsp27) was seen after viral infection in normoxia compared with hypoxia. Hsp27 knockdown or p38 inhibition reduced virus recovery, indicating that the p38 pathway has a role in the reduced efficacy of the γ 1 34.5-deleted virus in hypoxia. Taken together, these findings demonstrate that chimeric HCMV/HSV-1 efficiently targets both CD133+ GSCs and glioma cells in hypoxia.