BACKGROUND Sinonasal undifferentiated carcinomas (SNUC) are highly malignant and rare lesions. Therapeutic efforts often provide frustrating results. Their course is characterized by indolent progression, until it culminates in extensive local infiltration of adjacent anatomical structures or cervical lymphadenopathy in approximately one-third of patients upon admission. It most frequently affects males, with a sex ratio of 3: 1. The age at manifestation tends to be about 40-50 years. CASE REPORT We report the case of a 41-year-old man with intracranial expansion of SNUC. Two previous sinus surgeries were performed endoscopically because the lesion at that moment was exclusively located endonasally. Within the last few months, he had been having persistent headaches. Magnetic resonance imaging (MRI) revealed an anterior cranial fossa lesion. Therefore, he underwent a bifrontal craniotomy and excision of the space-occupying lesion (SOL). The osseous defect of the skull base was covered with a titanium mesh. Finally, we performed a duraplasty using a pericranial flap and fat tissue taken from his abdomen. Postoperatively, his wound was dehisced. We proceeded then to a frontal craniectomy with surgical debridement, subgaleal empyem and epidural abscess removal, and copious irrigation with oxygen peroxide. Enterococcus spp. were isolated from pus cultures. Despite receiving bacteria-focused antibiotics, he unfortunately developed sepsis and died. The histopathologic findings revealed a SNUC, which is the criterion standard for diagnosis. CONCLUSIONS Multimodal treatment offers the best prognosis to patients with SNUC. Combined operations by otolaryngologists and neurosurgeons provide the necessary radicality. There is high risk of wound healing disorders, especially when local irradiation had been administered.