An extremely rare case of in situ adenocarcinoma of the uterine cervix that developed into invasive cancer is reported. The patient was a 54-year-old Japanese female who complained of vaginal spotting. Pelvic examination revealed no abnormalities and routine Papanicolaou smear was misinterpreted as negative. Multiple wedge biopsies of the uterine cervix were done because Papanicolaou smears taken after 7 months were reported as suspicious. The wedge biopsy revealed dysplastic changes of the endocervical glands. It was diagnosed as being in situ adenocarcinoma by a later review. The patient was examined by cytology and colposcopy every 3 to 12 months. An advanced adenocarcinoma was found in the uterine cervix after 5 years. Total abdominal hysterectomy, resection of the vagina and cardinal ligament, and postoperative irradiation were performed. The patient is alive and well at this writing. This is the second case of in situ adenocarcinoma of the uterine cervix that developed into invasive cancer.