To evaluate the prevalence and risk factors for adenomyosis, the clinical records of consecutive women undergoing hysterectomy during a 3 year period were retrieved. Data were collected on indication for the intervention, general sociodemographic characteristics of the patients, age at menarche, parity, abortions, and menopausal status at surgery. Adenomyosis was diagnosed in 332 of the 1334 cases (24.9%). The condition was present in 146 of the 627 patients (23.3%) with fibroids and menorrhagia, 68 of the 265 (25.7%) with prolapse, 21 of the 98 (21.4%) with ovarian cysts, 19 of the 100 (19%) with cervical cancer, 31 of the 110 (28.2%) with endometrial cancer, 16 of the 57 (28.1%) with ovarian cancer, and 19 of the 77 (24.7%) with miscellaneous indications. These differences were not statistically significant (chi 2(6) = 11.14). In comparison with nulliparous women, the odds ratio was 1.3 and 1.5 respectively in women with one and > or = two births (chi 2(1) trend = 5.76 P < 0.05). No relationship was found between age at surgery, age at menarche, indications for surgery, menopausal status at intervention, and presence of endometriosis. Our findings do not support the notion that adenomyosis is more frequently related to particular clinical conditions, and suggest that parity may be associated with an increased frequency of adenomyosis.