In women of fertile age, iron loss consequent to excessive menstrual discharge is by far the most frequent cause of iron-deficient anemia. However, the relationship between menstrual discharge and iron loss is poorly understood. In this prospective study, total menstrual and iron losses were assayed in a large cohort of non-anemic women and women with excessive menstrual blood losses (menorrhagia) in order to provide data useful for intervention. One hundred and five Caucasian women aged 20-45 years were recruited. Blood cell count and serum ferritin (SF) levels were determined in each case before menses. Menstrual fluid losses (MFL) were determined using a standardized pads' weight method. Hematin concentration was assayed by a variant of the Alkaline Hematin Method from which iron concentration was calculated. Mean SF levels were 36.2 (range 8.6-100) ng/ml in healthy women and 6.4 (range 5-14) ng/ml in patients with menorrhagia. Median values of iron lost/cycle were 0.87 mg in healthy women and 5.2 mg in patients with menorrhagia (ranges 0.102-2.569 and 1.634-8.665 mg, respectively, p < 0.001). In women with menorrhagia, iron lost/cycle strongly correlated (0.789, p < 0.001) with MFL. In conclusion, healthy women with normal menses lose, on average, 1 mg iron/cycle. Average iron losses in patients with menorrhagia are, at least in our cohort, on average, five-to-six times higher than normal. Most women with menorrhagia had totally depleted iron stores. Indirect, quantitative evaluation of iron lost with menses may be useful to assess the risk of developing iron-deficient anemia in individual patients.