Objective: The Japan Society of Obstetrics and Gynecology conducted a retrospective multi-institutional survey of patients who underwent cervical conization in Japan. This study aimed to determine the predictive factors for positive surgical margins in cervical intraepithelial neoplasia grade 3 (CIN 3) patients after therapeutic cervical conization and those for positive margins in patients who did not experience recurrence and did not undergo additional treatment. Methods: In 2009 and 2013, 14,832 patients underwent cervical conization at 205 institutions in Japan. Of these, 8856 patients who underwent therapeutic conization fulfilled the inclusion criteria. Their histologic findings and clinical outcomes were evaluated based on standard statistical procedures and clinical and demographic characteristics. Results: Negative and positive margins were observed in 7,585 and 1,271 (14.4%) patients, respectively. The predictors of positive margins were menopausal status (p<0.001), loop electrosurgical excision procedure (p<0.001), and Shimodaira-Taniguchi (S-T) conization (p<0.001). Of 1,271 patients with positive margins, 1,060 underwent no additional treatment; among those 1,060 patients, 129 (12.2%) experienced recurrence. The predictors of positive margins in patients who did not undergo additional treatment and did not experience recurrence were age, parity, gravidity, S-T conization, and laser scalpel conization. Conclusion Menopausal status and treatment procedures were associated with positive margins after therapeutic conization of CIN 3. It is important to understand the characteristics of treatment procedures and select an appropriate procedure for each case. For elderly or menopausal patients with positive margins, immediate additional treatment is recommended.