OBJECTIVE: To study whether a treatment of cervical intraepithelial neoplasia (CIN) is associated with an adverse outcome in the subsequent pregnancies. METHODS: This study is a register-based retrospective cohort study from Finland. National data of 25,827 women having a surgical treatment of the cervix for CIN in 1986-2003 and their 8,210 subsequent singleton births in 1987-2004 were studied. Main outcome measures were preterm birth rate, low birth weight rate, and perinatal mortality rate. RESULTS: The risk of any preterm delivery (less than 37 weeks of gestation), especially the risk of very preterm delivery (28-31 weeks of gestation), and extremely preterm delivery (less than 28 weeks of gestation) was increased after cervical conization (relative risk [RR] 1.99, 95% confidence interval [CI] 1.81-2.20; RR 2.86, 95% CI 2.22-3.70; and RR 2.10, 95% CI 1.47-2.99, respectively). After cervical ablation, the risk of preterm delivery was also increased. The risk of low birth weight and perinatal death was increased after conization (RR 2.06, 95% CI 1.83-2.31 and RR 1.74, 95% CI 1.30-2.32, respectively). Adjusting for maternal age, parity, and maternal smoking did not affect our results. CONCLUSION: Any treatment for CIN, including loop electrosurgical excision procedure, increases the risk of preterm delivery. It is important to emphasize this when treating young women with CIN. LEVEL OF EVIDENCE: II.