Adenomyosis was present in 161 of 1619 consecutive hysterectomy specimens. Adenomyosis coexisted with other pelvic pathology in 97 women and was the only histologic finding in 64 women. Most patients were 35 to 50 years of age, parous, white, had not taken steroid hormones, had not had uterine surgery, and complained of abnormal uterine bleeding and/or pelvic pain. Adenomyosis was most associated with leiomyomata, endometrial hyperplasia and carcinoma, and endometriosis. The clinical signs of uterine enlargement and tenderness were rarely observed. The diagnosis was suspected preoperatively in 10% of women. At surgery, adenomyosis was not recognized in 65% of patients. Adenomyosis is a disease of unknown etiology whose uncharacteristic clinical profile and frequent association with more obvious pelvic pathology make it a neglected diagnosis.