Cervical cancer is about 6 times more frequent in Ecuador than in Japan. We investigated the association between infection by the human papillomavirus (HPV) and the genesis of cervical cancer in specimens of lesions of the cervical epithelium obtained from patients in Ecuador and Japan. We also examined the results of HPV DNA detection and typing by the polymerase chain reaction (PCR) performed under the same technical conditions in areas with differing rates of cervical cancer. Purified tissue DNA from paraffin-embedded samples was amplified by PCR with universal and type-specific primers. HPV DNA was detected in 8 (20%) of 40 normal cervical epithelial samples from Ecuadorian patients, 19 (45%) of 42 low-grade squamous intraepithelial lesions (LSIL), 16 (50%) of 32 high-grade squamous intraepithelial lesions (HSIL), and 38 (81%) of 47 invasive squamous cell carcinomas (SCC) compared with 3 (10%) of 30 normal cervical specimens from Japanese patients, 107 (51%) of 210 HSILs, and 45 (71%) of 63 SCCs. The prevalence of HPV types 16 and 18 rose significantly with increasing histological grade (p<0.05). The prevalence of HPV DNA decreased with increasing age in both Ecuadorian and Japanese patients. The detection rate and type-specific distribution of HPV DNA were not correlated with geographic location. Findings suggest that risk factors associated with poverty and under-development may influence the prevalence of HPV infection and the sequence of events after HPV infection culminating in cervical cancer. These factors may help to explain the differing geographic distribution of this disease.