Recently, detection of human papillomavirus (HPV)mRNA expression was made possible by in situ hybridization. We described a patient with cervical intraepithelial neoplasia (CIN) 3, showing a distinctive and rare form of co-infection with HPV type 16 and 18. HPV-16 was detected in high grade squamous intraepithelial neoplastic lesion (CIN 3) and HPV-18 was in low grade lesion just adjacent to the HPV-16 infected area. This case suggests that HPV infection may be one of the most responsible causative agents producing malignant transformation and two distinctive HPV types can also simultaneously infect the squamous epithelium of the uterine cervix.