Sixty different types of human papillomavirus (HPV) are currently recognized. Of these, HPV types 1, 2, 4, 6, 7, 11, 13, 16, 18, 30, 32 and 57 have been identified in oral squamous cell lesions. The prevalence and incidence of clinical HPV infections of oral mucosa are incompletely established, and the figures on subclinical and latent infections are completely lacking. Similarly, no data exist on transmission of oral HPV infections. A long-term prospective follow-up study was started to assess the oral mucosal changes related to HPV infection in women with genital HPV infections. The aim was to elucidate whether genital HPV infections predispose the oral mucosa to this virus. This study reports the clinical, histologic and cytologic findings of oral mucosa as related to the genital status of 334 women prospectively followed-up in Kuopio University Central Hospital since 1981. At the time of examination, 5% presented with hand warts. Clinical wart in oral cavity was found in three patients (0.9%) only. Oral mucosa was clinically normal in 207 of 334 (62%) patients examined. Biopsies (n = 255) were taken from the buccal mucosa beneath the linea alba and above the sulcus in the region of the first molar, or from a lesion whenever present. Cytologic scrapings were taken from both sides of the buccal mucosa. Koilocytes were found in 0.9% of the cytologic scrapings, and in 9.4% of the biopsies. Altogether, four squamous cell papillomas and five flat condylomas were found in the biopsies. Morphologic changes suggestive for HPV were present in 25 biopsies. Hyperkeratosis proved to be a frequent finding (34%) in these biopsies.(ABSTRACT TRUNCATED AT 250 WORDS)