Schneiderian inverted papillomas may be troublesome lesions for clinicians with propensity for recurrences. Dysplasia is not uncommonly seen, and some of these lesions do progress to develop squamous carcinoma. The authors hybridized in situ seven inverted papillomas with RNA probes to human papillomavirus (HPV) 6, 11, 16, and 18. Four of these contained dysplasia, two were without dysplasia, and one contained invasive squamous cell carcinoma. Five inverted papillomas showed evidence of HPV infection based on hybridization. One with mild to moderate and one with severe dysplasia, and one without dysplasia hybridized with mixed probe HPV 6/11. One with mild dysplasia and one associated with invasive squamous cell carcinoma hybridized with mixed probe HPV 16/18. One inverted papilloma without dysplasia and one with severe dysplasia did not definitively hybridize with either mixed probe. These findings raise interesting questions as to role of HPV 6/11 and 16/18 in the development of inverted papillomas, and probably on the progression to and carcinoma.