Olfactory neuroblastoma (ONB) is a rare neoplasm of the head and neck region that is included in the differential diagnosis of other sinonasal tract malignancies. We studied the usefulness of using p63 as an aid in the diagnosis of ONB and other tumors of the sinonasal region. The specimens were 14 ONBs; 4 nasopharyngeal carcinomas (NPCs), nonkeratinizing subtype; 2 NPCs, undifferentiated subtype; 10 sinonasal undifferentiated carcinomas (SNUCs); 7 malignant melanomas; and 2 extranodal natural killer (NK)/T-cell lymphomas. We observed p63 expression in 5 ONBs (36%), 4 nonkeratinizing NPCs (100%), 1 undifferentiated NPC (50%), 2 SNUCs (20%); 0 malignant melanomas (0%); and 1 extranodal NK/T-cell lymphoma (50%). While all cases of NPC with positive staining for p63 showed strong and diffuse immunoreactivity, the ONB, SNUC, and lymphoma cases with positive immunoreactivity showed only focal staining for p63. No p63 expression was observed in malignant melanoma. We think p63 is a useful marker to help distinguish nonkeratinizing or undifferentiated NPC subtypes from various sinonasal tract malignancies. In particular, p63 helps distinguish nonkeratinizing and undifferentiated NPC subtypes from SNUC.