Objective: To determine if carbon dioxide laser conization of the cervix is a risk factor for preterm delivery in subsequent gestations and to evaluate whether there is any relationship between cone height and duration of pregnancy. Methods: Patients of fertile age who had carbon dioxide laser conization were followed for reproductive events. Cases were matched one-to-one with controls for known risk factors for preterm delivery. Pregnancy duration, rate of preterm birth, and mode of delivery were studied. Parametric and nonparametric tests were used for statistical analysis. Logistic regression analysis and Cox proportional hazard modeling were used to investigate the relationship between cone height and subsequent preterm delivery. Results: Sixty-four women with singleton pregnancies after carbon dioxide laser conization and 64 controls were included in the study. Overall, no difference was found in the rate of preterm delivery and duration of pregnancy. However, women with cone height of at least 10 mm had a higher rate of preterm delivery than either those with cone height less than 10 mm (five of 23 versus one of 41, P = .01) or the controls (five of 23 versus three of 64, P < .05). Cone height of at least 10 mm remained significant in predicting the occurrence of preterm delivery and the duration of pregnancy after adjusting for known risk factors (odds ratio 11.1, P < .05). Conclusion: Cone height of at least 10 mm is an independent risk factor for the duration of pregnancy and for the occurrence of preterm delivery in the subsequent gestation.