Objective: To study whether low serum ferritin (s-ferritin) levels are associated with recurrent pregnancy loss (RPL), and whether low s-ferritin predicts the risk of another pregnancy loss or the ability to conceive. Design: Cohort study. Setting: Fertility clinic at a university hospital. Patient(s): Eighty-four women referred to the RPL Unit and 153 women of reproductive age with no known fertility problem. s-Ferritin levels were measured in serum samples taken before pregnancy attempt. Intervention: None. Main Outcome Measure(s): s-Ferritin levels were correlated to pregnancy history, ability to conceive, and time to conception during the first 2 years after sampling. Furthermore, s-ferritin levels were correlated to outcome of the first pregnancy after referral for RPL. Result(s): Women with RPL had lower s-ferritin than the comparison group, 39.9 μg/L versus 62.2 μg/L, and had a higher prevalence of low iron stores (s-ferritin <30 μg/L), 35.7% versus 13.7%. We found an inverse relationship between s-ferritin level and number of pregnancy losses before referral. We did not find s-ferritin level to be associated with ability to conceive or time to pregnancy in either group. Nor did s-ferritin level predict the risk of losing the first pregnancy after referral for RPL. Conclusion(s): The inverse relationship between s-ferritin levels and previous pregnancy losses suggests that low s-ferritin is associated with a more severe reproductive disturbance in women with RPL. Whether low s-ferritin is causally related to RPL and if such women could benefit from iron supplementation to achieve a live birth warrants further investigation.