This study determined the presence of human papillomavirus (HPV) DNA in oral mucosa cells from 121 patients with different types of oral mucosal lesions (13 squamous cell carcinomas, 59 potentially malignant lesions, 49 benign erosive ulcerative lesions) and from 90 control subjects. HPV DNA was detected by nested polymerase chain reaction, and genotype was determined by DNA sequencing. HPV prevalence was 61.5% in carcinomas, 27.1% in potentially malignant lesions, 26.5% in erosive ulcerative lesions, and 5.5% in control subjects. The risk of malignant or potentially malignant lesions was associated with HPV and was statistically significant. HPV-18 was found in 86.5% of HPV-positive lesions but was not associated with a particular type of lesion and was found in 80% of the HPV-positive control subjects. HPV infection was related to older age but not to sex, smoking, or alcohol use; the presence of lesions in the oral cavity increased the risk of HPV infection.