OBJECTIVE: Cervical cancer is the second leading cause of cancer mortality among Mexican women aged 20-39 years, driven primarily by persistent human papillomavirus (HPV) infection. To determine the prevalence of high-grade squamous intraepithelial lesions (HSIL) in women under 40 years of age and identify associated risk factors. MATERIAL AND METHODS: An observational, cross-sectional study was conducted, including 359 women under 40 years old who were evaluated at the Gynecology and Obstetrics Medical Unit of Centro Médico Nacional de Occidente. Cervicovaginal cytology results indicative of HSIL were analyzed to determine prevalence and assess correlations with demographic and gynecological factors. RESULTS: The prevalence of HSIL was 39%, with the highest proportion of cases observed in women aged 35-39 years. The average age of sexual debut was 18.5 years, with an average of 2.93 sexual partners. Women diagnosed with HSIL were more likely to be older, married, and homemakers. HPV infection was highly prevalent across both low-grade squamous intraepithelial lesion and HSIL groups. CONCLUSION: A high prevalence of HPV infection was found, mostly in a relatively young population. A significant association between infection and risk factors, like marital status and gynecological/obstetric history, was also demonstrated. The findings also confirmed a relationship between HPV and HSIL.