As survival rates have improved in pediatric patients with leukemia, late side effects from chemotherapeutics and radiotherapy have become important considerations. We investigated these side effects and evaluated their impact on neurocognitive functions. The observational study included 68 patients with acute leukemia who were treated at Eskisehir Osmangazi University Medical Faculty. The study also included 62 of the patients' closest age siblings as a control group. Demographic and clinical data, chemotherapy protocol, use of radiotherapy were recorded, neurological and ophthalmological examinations, cranial imaging, electroencephalography, visual evoked potential, and hearing investigations were performed, and neurocognitive functions were evaluated. At least one or more late effects detected by a neurologic abnormality on physical exam, cranial magnetic resonance imaging, neurological tests, or neurocognitive tests was significantly more likely in the patient group (82.4%) compared to the control group (29%, p < 0.001). A higher rate (82.4%) of delayed neurological and cognitive problems occurred in children who received radiotherapy, intrathecal and/or systemic chemotherapy during leukemia treatment compared to age-matched siblings. Patients being treated for leukemia should be periodically evaluated for treatment-related side effects. Prophylactic interventions such cognitive training and maintenance of academic growth may offer the best hope of preventing late effects.