Background: Radiotherapy is used in the treatment of nasopharyngeal carcinoma (NPC). The temporal lobes are at risk because they lie directly in the path of radiation beams; hence the effect of radiotherapy on cognitive functioning is a major concern. Aims: To investigate the effect of radiotherapy on cognitive functioning in nasophyingeal carcinoma patients. Materials & methods: A battery of neuropsychological tests consisting of attention, memory & learning and visuospatial functions was done on 20 patients before and after radiation therapy. Also computerized tomography (CT) was done in all cases. The results showed significant impairment in attention (p=0.0001), verbal fluency (p=0.05), visuospatial functions (p=0.005), and learning & memory. Conclusions: Radiotherapy for nasopharyngeal carcinoma shows significant decline on cognitive functioning.