Using paraffin embedded specimens taken from 32 patients with histologically benign nasosinal papillomas, we conducted nuclear DNA analysis by flow cytometry and studied the biological degree of malignancy in this disease. Aneuploidy, which is frequently observed in malignant tumors was not seen in any of these nasosinal papilloma cases. Age did not affect either S+G2M % or polyploid %, two parameters that reflect cell proliferation capacity. Both parameters, S+G2M % and polyploid %, were higher in inverted papillomas which are more likely to become malignant than epithelial papillomas. In recurrent cases of nasosinal papilloma both S+G2M % and polyploid % were higher than in nonrecurrent cases. Moreover, the polyploid % was significantly different, supporting speculation that this can be used as a parameter for predicting recurrence of nasosinal papilloma.