Objective: To evaluate the spontaneous progression of cervical intraepithelial neoplasia grade 2 (CIN2) in accordance with Chlamydia trachomatis (chlamydia) serology.Methods: A prospective observational study included women diagnosed with CIN2 by cervical biopsy and managed conservatively for 24 months at Hospital del Mar, Barcelona, between December 2011 and October 2013. Serum anti-chlamydia immunoglobulin G (IgG), previous cytology, and high-risk human papillomavirus (HPV) genotyping were recorded at baseline. The outcome was regression, persistence, or progression of CIN2.Results: Overall, 93 women aged 18-56 years were enrolled. Spontaneous regression was observed for 61 (66%) women, and 21 (23%) progressed to CIN3. Eight (9%) women had chlamydia seropositivity at baseline. Multivariate analysis showed that anti-chlamydia IgG seropositivity (odds ratio [OR], 19.1; 95% confidence interval [CI], 1.9-189.7), previous high-grade squamous intraepithelial lesion cytology (OR, 5.0; 95% CI, 1.7-14.6), and HPV16 (OR, 4.8; 95% CI, 1.7-13.7) increased the risk of CIN2 persistence or progression.Conclusion: Women with CIN2 and chlamydia IgG seropositivity had increased risk of progression to CIN2+ and immediate treatment may be recommended for these women. Larger clinical studies are needed to confirm the results, but chlamydia serology might be introduced into CIN2 management to better individualize treatment. [ABSTRACT FROM AUTHOR]