Background: Maximal safe resection is the treatment for most primary brain tumors. Depending on the type of tumor and extension of resection, further treatment may be required. The use of radiotherapy (RT) has changed from whole-brain to less invasive approaches, including gamma-knife and stereotactic radiosurgery. Radionecrosis and leukoencephalopathy have been identified as consequences of these treatments, affecting cognitive functions. The aim of this study was to conduct a systematic review on neurocognitive effects of RT in patients with primary brain tumors. Methods: A systematic search was done using different databases. Sixteen articles were analyzed including case-control, cross-sectional, case-series, case-report designs, use of surgery and RT or RT alone with post-therapy cognitive function assessment. Results: Cognitive function varied depending on the type of tumor and RT dose used. Higher deficits were reported in executive functions, verbal processing, attention, and memory. Other contributing factors in neuropsychological performance included major surgical morbidity, delayed diagnosis, age at diagnosis, type of RT used, number of interventions, size, type and localization of the tumor, and assessment time after treatment. Conclusions: Considering negative effects of RT in both children and adults with brain tumors, is important to better direct therapeutic interventions and consider strategies to detect and prevent the progression of these impacts.