Abstract: Objective：To investigate the natural history of CINⅠ lesions. Methods：548 patients were enrolled into the cohort. They were followed up for 24-48 months without any treatment. Every 6 to 12 months， the patients were called back to have the Liquid-based Cytological Test and High-risk Human papillomavirus Test（HC-Ⅱ）. If the LCT was ASCUS and HR-HPV was positive or LCT was higher than ASCUS， then colposcopy was used to assess the disease situation and multi-point biopsies were made at the same time. The biopsy results were the gold standard to assess the outcome if it was progression， resistance or regression. Results： ①The 36 months dropout rate was 10.22%. ②At the end of the follow-up， 16 patients had progressed to higher grade lesions， including 11 CINⅡ and 5 CINⅢ. No one had progressed to invasive cervical cancer. 29 patients whose CINⅠ lesions had resistant and 477 patients had regressed. Within 6 months， the CINⅠ progression rate， resistance rate and regression rate was separately 0.57%， 67.05%， and 37.36%. Within 12 months， the CINⅠ progression rate， resistance rate and regression rate was separately 1.15%， 48.08%， and 55.56%. Within 24 months， the CINⅠ progression rate， resistance rate and regression rate was separately 2.30%， 20.88%， and 77.20%. Within 36 months， the CINⅠ progression rate， resistance rate and regression rate was separately 3.07%， 5.56%， and 85.63%. ③The 6， 12， 24， 36 months HR-HPV cultivate clearance rate of HR-HPV positive CINⅠ was separately 52.76%， 61.84%， 82.64%， and 94.52%. Conclusions： ① Most of the CINⅠ lesions （85.71%） can regress themselves during 36 months， only few part（3.07%） of them will progress to high grade lesions. The cultivate progression rate and regression rate became higher and higher along with the time during the 36 months follow-up. ②The cultivate rate of HR-HPV clearance became higher and higher with the time during the 36 months follow-up. ③CINⅠ were caused by transient HR-HPV infection，HR-HPV positive CINⅠ lesions had the same regression trend with HR-HPV clearance.

Key words: Cervical intraepithelial neoplasia, Precancerous conditions, Papillomaviridae, Cytodiagnosis, Uterine cervical neoplasms