Sinonasal Undifferentiated Carcinoma (SNUC) is a very rare, highly aggressive malignant tumor of the nasal cavity and paranasal sinuses. SNUC tends to present with advanced-stage disease, often with intracranial invasion. It requires an aggressive multimodality therapy that includes surgical resection. A cure rate of less than 20% is generally reported in the literature, with most patients dying within 1 year of onset of the disease. Three patients diagnosed as SNUC were treated at the Yeungnam University Medical Center between the years 2000 and 2003 were analyzed retrospectively. All patients presented with the disease very advanced. The three cases were given chemotherapy or chemotherapy with radiotherapy. Two patients died of the disease, surviving only 6 and 11 months following treatment, respectively. We did a follow-up on just the one remaining case with incomplete controlled disease for 27 months. The overall prognosis of SNUC is very poor. We consider that more intensive multimodality therapies are recommended for all patients with SNUC.