Introduction Nasal polyposis (NP) is considered to be the state of chronic inflammation of nasal mucosa and sinuses presenting with various nasal symptomatology. In most cases, it is treated conservatively. Recently, functional endoscopic sinus surgery (FESS) was developed as the valuable and advantageous surgical procedure to treat NP. Despite the inherited risks of this procedure, its complication rate is considered to be acceptable compared to potential benefits for the patient. Case Fifty-five-year-old man was admitted to the hospital for surgical removal of the nasal polypus. After the usual pre-surgery procedures, the patient underwent FESS. Under general anesthesia, left sphenoid sinus was opened and cleaned from the imflammatory discharge, polypus was excised, and following the trepanation the left maxillary sinus was left to drain out. Polypus and pieces of sinonasal mucosa were sent to pathohistological analysis, which yielded in diagnosis of inverted sinonasal papilloma. The early postoperative recovery was regular, but 2h upon the surgery, the patient started to lose consciousness gradually falling into the state of coma. CT scan and angiography of the head revealed pneumocranium, defect of the left ethmoidal sinus, hematoma in the left frontal cerebral lobe, as well as the hemorrhage in all four cerebral ventricles. A series of neurosurgical procedures followed in the next 8 days. Despite the attempts to resolve above complications, the patient remained comatous and died 16 days after the polypectomy. Autopsy revealed the extensive oval-shaped defect on the skull base in the left posterior part of cribrous plate of the left ethmoid bone. The brain appeared swollen and heavily congested, showing the zone of subarachnoidal hemorrhage in basal face of left frontal lobe. Frontal serial sections revealed large intracerebral haematoma in basal periventricular structures of left frontal lobe extending to the whole ventricular system. Apart from the above, most prominent finding was bilateral bronchopneumonia. The cause of death was attributed to bronchopneumonia following the brain trauma, manner of death ruled as violent. Conclusion Although majority of the patients suffering from chronic rhinosinusitis or NP recover well after the endoscopic surgery, the possibility of undesirable outcome must not be ignored. This case calls for assessment of potential medical liability caused by malpractice. Having in mind rather high