Patients who survive retinoblastoma are at risk for developing additional malignant neoplasms, including tumors of the sinonasal tract. We report 2 cases of secondary sinonasal malignancy arising in pediatric patients previously treated for retinoblastoma, with features of neuroendocrine carcinoma. Both lesions were characterized by a proliferation of round to oval cells arranged in solid sheets, trabeculae, and nests, diffusely infiltrating nasal mucosa and bone tissue. Immunohistochemically, they were diffusely positive for epithelial markers, as well as for neuroendocrine markers and for TP53 and retinoblastoma gene products. TP53 gene analysis showed the presence of a missense mutation P72R (CCC/CGC) and a single nucleotide polymorphism P36P (CCG/CCA) in exon 4 in 1 case. Literature review revealed 5 previously reported cases, all showing primitive undifferentiated morphology with variable expression of neural and epithelial markers. These tumors represent a peculiar subset of undifferentiated sinonasal neoplasms with extremely aggressive clinical behavior.