Paraffin-embedded tissues of 42 sinonasal inverted papillomas were subjected to polymerase chain reaction using type-specific primers pairs of HPV 6, 11, 16, 18, and 33. Two cases of HPV 11 and one of HPV 6 were amplified in 36 samples of benign inverted papilloma, and two cases of HPV 16 were amplified in five samples of inverted papilloma with co-existing squamous cell carcinoma. Inverted papillomas recurred in 1 (16%) of 6 cases exhibiting dysplasia, and in 3 (10%) of 30 cases not exhibiting dysplasia. Inverted papillomas also recurred in 2 (66%) of 3 cases positive for HPV, and in 2 (6%) of 33 cases negative for HPV. These results suggest that HPV may be involved in the pathogenesis of inverted papillomas, may cause malignant transformation of inverted papillomas, and that there may be an apparent relationship between HPV infection and the recurrence of sinonasal inverted papillomas.