Epidemiological information on telomerase activity (TA) and development of cervical lesions is scarce. A nested case-control study was carried out within a cohort of Colombian women tested for Human Papillomavirus (HPV). Measurement of TA was done in cervical scrapes of 25 women who developed High Grade Squamous Intraepithelial Lesion (HGSIL) during the first 6 years of follow-up and was compared with that of 104 control women who maintained normal cytology during the entire follow-up. TA was measured by a telomerase repeat amplification protocol-ELISA. TA and HPV infections were significantly more frequent in cases than in controls. Likewise, 68% of the cases were positive for both TA and HPV compared with only 7.7% of the controls (P<0.0001). Factors independently associated with increased odds of HGSIL included TA, high risk HPV (hrHPV) infections and multiple parities. When restricted to hrHPV positive women, TA was strongly associated with increased odds of HGSIL (adjusted odds ratio=37.94, 95% confidence interval, 1.64-678.1). In addition to an infection with hrHPV, TA appears to be a significant cofactor for HGSIL.