The pathologic features and the behavior of 50 cases of adenocarcinoma (excluding adenoid cystic carcinoma and mucoepidermoid carcinoma) of the sinonasal tract are presented. The cases were divided on histologic grounds into 23 low-grade and 27 high-grade neoplasms. The low grade lesions had a well developed glandular pattern throughout, very uniform nuclei, and minimal mitotic activity. The high grade tumors had a less uniform glandular pattern, commonly with solid or sheet-like areas, manifested nuclear pleomorphism, and generally had a higher mitotic rate. The low-grade group had a prognosis markedly better than the high-grade group. Since the literature tends to consider all sinonasal adenocarcinomas as relentlessly progressive neoplasms with poor prognosis, it is important to recognize this category of low grade neoplasm in order that treatment and prognostication can be better related to their behavior.