The literature lacks studies of cognitive impairments in large groups of patients after resection of third ventricle colloid cysts. Objective. To evaluate cognitive impairments in patients before and after resection of third ventricle colloid cysts. Material and methods. We performed a clinical and neuropsychological study of 52 patients with third ventricle colloid cysts using the Luria method (1962). Forty three patients were examined before and after cyst resection in the early postoperative period (three patients in this group were also examined in a long-term period of 3―7 months after surgery). Forty one patients were operated on using the transcallosal approach, and two patients were operated on using the subtentorial-supracerebellar transchoroidal approach. The other patients were examined only before or after surgery. The patients’ age ranged from 14 to 61 years; the mean age was 33.8 years; the median age was 29 years. Results. On examination before surgery, cognitive impairments were minimal in 5 patients without clear signs of hydrocephalus. Impairments of memory and dynamic praxis, mild spatial disorders, and psychological inertia were observed in other patients with hydrocephalus. There was no significant difference in the state of cognitive functions between patients with and without stagnation in the fundus. On examination on day 3―6 after transcallosal surgery, several groups of patients were identified. Eight patients had an improvement in cognitive functions, which might be related to postoperative resolution of hydrocephalus. In 15 patients, changes in mnestic functions were insignificant. This group consisted of the youngest patients with a median age of 24 years. Korsakoff syndrome and disorientation were detected in 5 patients. This was the oldest age group, with a median age of 48 years. In other 13 patients, aggravation of mnestic disorders was moderate.Similar memory impairments were detected in the case of the subtentorial-supracerebellar approach. Memory disorders progressively regressed in all patients. Conclusion. Postoperative memory impairment of a varying degree was found in 21 out of 43 patients, with adhesions between the cyst capsule and fornix being observed only in 5 patients. In this case, no injury to the fornix was intraoperatively observed. We discuss the role of the age factor, cyst size, and technical surgical difficulties in the pathogenesis of memory disorders in the absence of injury to the calvarium during colloid cyst resection.