In order to estimate the frequency and risk factors for adenomyosis, the clinical records of 594 women undergoing hysterectomy were retrieved. Data were collected on indications for the intervention, age at surgery, age at menarche, parity, abortions, mode of delivery, abnormal uterine bleeding, dysmenorrhea, and menopausal status at surgery. Adenomyosis was found in 116 of the 594 patients (19.5%). A pathologic condition was present in 63 patients with fibroids (20.5%), 11 with genital prolapse (25.6%), 11 with benign ovarian tumors (17.8%), six with endometrial hyperplasia (13.6%), two with cervical cancer (18.2%), ten with endometrial cancer (16.1%), and 13 with ovarian cancer (21.3%). No relationship was found between adenomyosis and endometriosis. On the contrary, a strong relationship was found between adenomyosis and parity, cesarean section, induced abortions, dysmenorrhea, abnormal uterine bleeding, and late age at menarche. These results show that adenomyosis is a common pathologic finding, significantly related to reproductive and menstrual characteristics of the patients.