Objective. To determine the incidence and risk factors for the occurrence of iatrogenic defects in the skull base, develop recommendations for their prevention, and model approaches to the treatment of this complication. Material and methods. During the period from 2000 to 2017, 570 patients with nasal cerebrospinal fluid (CSF) drainage underwent surgical treatment at our institution. Of these 570 cases, 62 (11%) cases had an iatrogenic etiology. A retrospective analysis of the patients’ medical history, radiographic characteristics, defect type and localization, and methods of reconstruction has been conducted. Results. In the series of 62 patients, 32 (52%) patients had iatrogenic nasal CSF drainage after ENT surgery (including endoscopic surgery), 10 (16%) patients had defects after block resection of skull base structures, and 17 (27%) patients had skull base defects after neurosurgical interventions. The defects were mostly localized in the sphenoid sinus in 21 (34%) cases, the cells of the ethmoidal labyrinth in 15 (24%) cases, the cribriform plate in 14 (23%) cases, and the frontal sinus in 7 (11%) cases. Multiple defects were observed in 5 (8%) cases. All 62 patients underwent reconstructive surgery for a complex skull base defect using an endoscopic endonasal approach in 55 (89%) cases and a combined approach in 7 (11%) cases. The success rate of the reconstructive interventions was 87%. Conclusions. The risk of iatrogenic defects of the skull base depends on the experience of the surgeon, the extent of the radicality of the surgery, and the individual anatomical features of the patient. To prevent the occurrence of this complication, thorough knowledge of the topographic anatomy of the paranasal sinuses and the surgical parameters of the risk areas are required, as well as a meticulous preoperative analysis of the patient’s CT data. In cases of intraoperative nasal CSF drainage, it is necessary to inform the anesthesiologist, lower the head end of the table (for the prevention of pneumocephalus), maximize visualization of the basic anatomical landmarks, examine the typical places of damage to the skull base, identify the site of the fistula and perform surgical reconstruction. In cases of a surgeon’s insufficient experience in the diagnosis and treatment of this discussed pathology, the patient must be transferred to a specialized clinic.