Adenocarcinomas in situ (AIS) of the cervix represent less than 1% of all primary adenocarcinomas of the cervix; 11 cases from the Magee-Women's Hospital (1969-1984) are described. The patients' ages ranged from 25 to 81 years (average 48.5 years). One patient was nulliparous and the others had one to five children. The most common presenting symptom was postmenopausal or other abnormal vaginal bleeding. The AIS were diagnosed as follows: a positive, suspicious, or dysplastic Pap smear in seven cases; in three, the AIS was an incidental finding during a hysterectomy; and one case was diagnosed in an endocervical curettage. Most of the AIS were in or near the transformation zone, having two distinct histologic glandular patterns with tall columnar or large ballooned cells (Types I and II respectively). In three cases an associated in situ squamous cell carcinoma or severe dysplasia of the cervix was seen. Two patients had associated well-differentiated adenocarcinoma of the endometrium and a third had endometrial hyperplasia. One lesion stained strongly positive for carcinoembryonic antigen and all others were negative. Eight patients underwent total abdominal hysterectomy and bilateral salpingo-oopherectomy (TAH-BSO), two had total abdominal hysterectomy (one with salpingo-oophorectomy), and one 25-year-old was treated by deep conization only. All patients, except one who died with associated adenocarcinoma of the cecum, were alive 8 to 127 months after treatment.