A series of 343 consecutive cases with the preoperative diagnosis of carcinoma in situ of the uterine cervix treated by cervical conization is presented. In 93% of these patients cervical cytology returned to normal. The follow-up period ranged from 1 to 5 years. There was significantly greater chance for an apparent cure in cases in which histologic evaluation indicated free margins of resection (98%) than in those where the margins were involved by the neoplastic process (70%). Colposcopic evaluation to determine the site for punch biopsies and adequate resection margins could greatly enhance the success of therapeutic conization. The urgent need for conservative management of cervical intraepithelial neoplasia because of its predominance among young women is discussed.