The anatomic distribution of cervical adenocarcinoma in situ was ascertained in 23 cases of adenocarcinoma in situ, 10 of which also had "early" invasive adenocarcinoma. The adenocarcinoma in situ involved both surface and gland epithelia in all cases, involved a variable number of quadrants, involved glands beneath the transformation zone in about two thirds of cases, was multifocal only occasionally, extended up the endocervical canal for a variable distance (up to 30 mm), and was associated with squamous dysplasia in about half of cases. From this topographic outline of adenocarcinoma in situ, it is recommended that if cervical conization is chosen as conservative therapy for adenocarcinoma in situ the "cone" be cylindrical in shape, to include the transformation zone and deep glands, and extend at least 25 mm up the endocervical canal.