Abstract Background EORTC study 22033–26033 showed no difference in progression-free survival between high-risk low-grade glioma receiving either radiotherapy (RT) or temozolomide (TMZ) chemotherapy alone as primary treatment. Considering the potential long-term deleterious impact of RT on memory functioning, this study aims to determine whether TMZ is associated with less impaired memory functioning. Methods Using the Visual Verbal Learning Test (VVLT), memory functioning was evaluated at baseline and subsequently every 6 months. Minimal compliance for statistical analyses was set at 60%. Conventional indices of memory performance (VVLT Immediate Recall, Total Recall, Learning Capacity, and Delayed Recall) were used as outcome measures. Using a mixed linear model, memory functioning was compared between treatment arms and over time. Results Neuropsychological assessment was performed in 98 patients (53 RT, 46 TMZ). At 12 months, compliance had dropped to 66%, restricting analyses to baseline, 6 months, and 12 months. At baseline, patients in either treatment arm did not differ in memory functioning, sex, age, or educational level. Over time, patients in both arms showed improvement in Immediate Recall (P = 0.017) and total number of words recalled (Total Recall; P < 0.001, albeit with delayed improvement in RT patients (group by time; P = 0.011). Memory functioning was not associated with RT gross, clinical, or planned target volumes. Conclusion In patients with high-risk low-grade glioma there is no indication that in the first year after treatment, RT has a deleterious effect on memory function compared with TMZ chemotherapy.