Objective.:Several intratype variants of HPV16 and 18 have been identified. These variants are associated with populations from different geographic regions,and show a differential distribution among the severity of the cervical lesion,most likely due to different pathogenic potential. The objective of this study was to investigate the variant distribution of HPV16 and 18 in a Mexican population and its association with the severity of the cervical lesion and the histological lineage of cervical cancer. Methods.:HPV types 16 and 18 detection was performed in 412 samples of preinvasive and invasive specimens from patients attending a Primary Health-Care Center,an Early Cervical Lesion Clinic,or a Cancer Center. Distribution of HPV variants was correlated with the cytological findings and tumor cell types using contingency tables. Statistical difference was tested with the Fisher’s Exact Test or its Fisher Freeman-Halton extension for RXC tables. Alpha value was set at the P < 0.05. Results.:Among the 277 women included in this study without cancer,63.5%(176 cases) had a normal cytology; from the remaining 101 women,53.5%were LSIL (54 cases),and 46.5%HSIL (47 cases). From a total of 135 invasive carcinomas,78.5%were squamous (106 cases); 6.6%adenocarcinoma (9 cases); 9.6%adenosquamous (ADSC) (13 cases); and 5.1%were undifferentiated carcinoma (7 cases). HPV16 E and AA-a were evenly distributed among preinvasive and invasive lesions. However,the isolate AA-c was exclusively found in cervical cancer. HPV18 Var-1(E) was almost exclusively found in invasive lesions,while the HPV18 Var-2(Af) predominated in normal or preinvasive lesions. In invasive cancer,this variant was found only in squamous tumors. Conclusions.:The differential distribution of HPV16 and 18 variants in cervical lesions we found further supports experimental data on the different pathogenic potential of HPV16 and 18 variants for cervical cancer development. These variants are associated with populations from different geographic regions, and show a differential distribution among the severity of the cervical lesion, most likely due to different pathogenic potential. The objective of this study was to investigate the variant distribution of HPV16 and 18 in a Mexican population and its association with the severity of the cervical lesion and the histological lineage of cervical cancer. Methods. HPV Types 16 and 18 detection was performed in 412 samples of preinvasive and invasive specimens from patients attending a Primary Health-Care Center, an Early Cervical Lesion Clinic, or a Cancer Center. Distribution of HPV variants was correlated with the cytological findings and tumor cell types using contingency tables. Statistical difference was tested with the Fisher’s Exact Test or its Fisher Freeman-Halton extension for RXC tables. Alpha value was set at the P <0.05. Resu Of the remaining 101 women, 53.5% were LSIL (54 cases), and 46.5% HSIL (47 cases). From the remaining 101 women, 53.5% were in this study without cancer, 63.5% (176 cases) had a normal cytology; A total of 135 invasive carcinomas, 78.5% were squamous (106 cases); 6.6% adenocarcinoma (9 cases); 9.6% adenosquamous (ADSC) (13 cases) -a were evenly distributed among preinvasive and invasive lesions. However, the isolate AA-c was exclusively found in cervical cancer. HPV18 Var-1 (E) was more exclusively found in invasive lesions while the HPV18 Var-2 (Af) predominated in normal or preinvasive lesions. In invasive cancer, this variant was found only in squamous tumors. Conclusions .:The differential distribution of HPV16 and 18 variants in cervical lesions we found further supports experimental data on the different pathogenic potential of HPV16 and 18 variants for cervical cancer development.