ObjectiveTo assess menstrual blood loss and other menstrual characteristics prospectively in women with and without endometriosis.MethodsThree hundred fifteen premenopausal women undergoing laparoscopy for various reasons were asked to complete a pictorial blood loss assessment chart devised by Higham et al to evaluate menstrual flow on which the monthly score has been demonstrated to correlate directly with uterine blood loss measured by the alkaline hematin method. In addition, cycle length and flow duration were recorded. The women also were asked to grade dysmenorrhea severity using a 100-mm visual analogue and a 0-3-points verbal rating scale.ResultsOne hundred sixty-three women had endometriosis, and 152 did not. The latter group comprised 59 women with a normal pelvis, 36 with nonendometriotic ovarian cysts, 29 with chronic pelvic inflammatory disease, and 28 with miscellaneous conditions. The median [interquartile range] pictorial blood loss assessment chart score was 110 [66.5–156.5] in women with endometriosis and 84 [56–129] in those without the disease (P= .007); 87 out of 163 (53%) women with endometriosis had a menstrual chart score equal to or greater than 100 compared with 56 out of 152 (37%) of those without (χ21= 8.02,P= .005; difference = 16%, 95% confidence interval, 6%, 28%). Menstrual flow duration was slightly longer in women with endometriosis (mean difference, 0.33 days). Dysmenorrhea visual analogue and verbal rating scores were significantly higher in the endometriosis than the nonendometriosis group.ConclusionAccording to a visual chart, women with endometriosis had heavier menstrual flow and a significantly higher rate of abnormal menstrual scores than those without the disease.