The clinical and pathologic features of schneiderian papillomas were studied in 67 patients. There were 40 male and 27 female patients, and the mean age at diagnosis was 49 +/- 17.9 (SD) years. Nasal obstruction or perception of a nasal mass was the most common presenting symptom; mean duration of symptoms was 10.8 +/- 15.8 (SD) months. Almost equal numbers of papillomas had predominantly endophytic (inverted) (n = 32) and predominantly exophytic (fungiform) (n = 30) patterns, and five had mixed patterns. Multiple morphologic variables were evaluated in the initial specimens, including cytologic atypia and number of mitotic figures; there were no statistically significant correlations between these variables and biologic behavior. Of the 39 patients for whom follow-up information was available (mean follow-up period, 38.6 months), six patients (all with predominantly endophytic patterns) had copresented with schneiderian papillomas and carcinomas. The remaining 33 patients initially had only benign schneiderian papillomas. In these 33 patients, recurrences developed in 11 (33 per cent), local invasion in two (6 per cent) (both with inverted papillomas), and epidermoid carcinoma in one (3 per cent) (with an inverted papilloma). Three patients had evidence of disease when last examined, and two patients had died of disease (both after copresentation with schneiderian papillomas and carcinomas). The continued use of the term inverted papilloma (endophytic pattern) as a specific subset of schneiderian papillomas is recommended, as all serious complications, including progression to local invasion, copresentation with carcinoma, and development of carcinoma, were associated with these lesions.