One hundred and sixty-two cases of Stage IA microinvasive carcinoma of the cervix are presented. These patients represent the combined experience at the University of Miami School of Medicine, Miami, Florida, and Downstate Medical Center, Brooklyn, New York. The criteria used in both institutions are 1) penetration of invasive carcinoma beneath the basement membrane of less than 1 mm and 2) absence of invasion of blood vessel or lymphatic spaces. All tissue specimens have been measured accurately by use of calibrated optics. The literature has been reviewed for criteria of diagnosis of microinvasive cancer, as well as methods of management. Our method of accurately determining depth of penetration is described and the evolution of microinvasive cancer is presented in a series of photomicrographs in which measurements are accurate to 0.1 mm. In the literature, when depth of penetration of up to 5 mm is used as criterion for microinvasive carcinoma, the incidence of nodal metastasis may be as high as 3.5%. Since, in our combined institutions, the mortality rate with radical hysterectomy is less than 1% and the incidence of ureterovaginal fistulas is 1.2%, we conclude that simple hysterectomy is not adequate therapy for lesions with stromal invasion to a depth of 5 mm.