What are the criteria for the microscopic diagnosis of carcinoma in situ of the cervix? What evidence has been produced to indicate a relationship between carcinoma in situ and invasive cervical cancer? How should the preinvasive lesion be treated? These three questions are discussed, and clinical experience is presented based on 350 cases of carcinoma in situ in which hysterectomy was performed. None of the 350 women have died of cervical cancer.