Nonintestinal sinonasal adenocarcinomas (SNACs) are somewhat poorly characterized and high-grade nonintestinal SNACs have been only rarely reported. Here, we review our experience with these tumors. Twenty-seven cases of high-grade nonintestinal SNACs were identified from 22 men and 5 women. Ages ranged from 22 to 83 years (mean±1 standard deviation=54.7±18.6 y; median=60 y). Thirteen cases involved the nasal cavity and sinuses, 10 involved the nasal cavity only, and 4 involved sinuses only. Most cases had marked cytologic and nuclear pleomorphism, abundant mitotic activity, and necrosis; however, these features were not uniform. Although histologically heterogeneous, recurrent growth patterns were seen that resembled other neoplasms of the area. Tumors lacked CDX2 and CK20 immunoreactivity (aside from rare CK20 immunoreactive cells). High-grade nonintestinal SNACs are more common in men and, although they occur over a wide age range, they are much more common in older individuals. Histologically, they show a great deal of heterogeneity.