Thirty-six consecutive cases of adenocarcinoma in situ (ACIS) of the uterine cervix, including 8 cases of early stromal invasion to a depth not exceeding 5 mm, were revised with specific reference to detection rate and treatment. The final histologic diagnoses were based on 31 cone biopsies, 1 hysterectomy specimen, and 4 endocervical curettings/punch biopsies. ACIS was localized in the transformation zone of all cone biopsies/hysterectomy specimen, with a mostly superficial spread in the glands. The mucosal surface was involved in 34 cases. In 29 cone biopsies, ACIS was found unifocal. ACIS was associated with lesions of the squamous epithelium, mostly severe, in 25 cases. On review, all cervical smears were positive and ACIS could be specifically diagnosed in 24 cases. Pretreatment biopsies showed ACIS in 28 cases. Detection of early invasive adenocarcinoma required cone biopsy in most cases. Colposcopy showed no characteristics of ACIS. The detection of ACIS depended on the extension of the lesion. Conization with uninvolved margins was an adequate treatment. Residual ACIS was only found in cases with coexisting early invasive adenocarcinoma. No recurrences or frankly invasive adenocarcinomas have been observed during the observation period.