Objective: To measure the influence of uterine size on the risk of operative complications among women undergoing abdominal hysterectomy for uterine leiomyomas. Methods: Four hundred forty-six women undergoing abdominal hysterectomy for pathologically confirmed leiomyomas were analyzed using data from a previously reported prospective cohort study. We compared the risk of operative complications among women with uterine weights less than 250 g, 251-500 g, and greater than 500 g. Logistic regression was used to estimate the independent effect of uterine size on the probability of operative complications. Results: The risk of blood transfusion increased with increasing uterine weight; 13.7, 14.2, and 26.7% of women with uterine weight less than 250 g, 251-500 gr and greater than 500 g, respectively, required transfusion (P for trend < .05). After adjustment for race, previous surgery, preoperative weight, concurrent endometriosis, and type of insurance coverage, women with uterine weight greater than 500 g had increased odds of having a transfusion (odds ratio [OR] 2.4, 95% confidence interval [CI] 1.3-4.3). These women also had increased odds of having an estimated blood loss greater than 500 mt (OR 2.5, 95% CI 1.5-4.2), vaginal cuff cellulitis (OR 2.8, 95% CI 1.3-6.2), and at least one of a number of operative complications (OR 1.6, 95% CI 1.0-4.0). Conclusion: Women with leiomyomas whose uterine weight exceeds 500 g have an increased risk of complications from abdominal hysterectomy.