We report a rare case of sinonasal inverted papilloma (IP) associated with small cell neuroendocrine carcinoma (SNEC). To our knowledge, this is the first report to describe SNEC found during the treatment of sinonasal IP. Surgery and five cycles of cisplatin plus etoposide with concurrent intensity modulated radiation therapy were performed. Neither local recurrence nor distant metastasis was noted during 6 years of post-diagnostic follow-up. The prognosis of SNEC is very poor. Treatment planning for sinonasal IP should consider a possible association with this rare but aggressive malignancy, whose treatment is completely different from that of squamous cell carcinoma, a malignancy which is commonly associated with IP. We also performed a PubMed review of the literature to identify the incidence and pathological diagnosis of associated malignancy. Among a total of 5286 cases of sinonasal IP (61 studies), the incidence of associated malignancy was 8.02% in squamous cell carcinoma, 0.19% in transitional cell carcinoma, 0.04% in mucoepidermoid carcinoma, 0.02% in verrucous cell carcinoma and 0.02% in adenocarcinoma. The incidence of associated malignancy was significantly higher in East and Southeast Asia (11.0%) and North America (10.4%) than in Europe (3.9%) (p=0.04 and p=0.03, respectively; T-test).