Iron deficiency in patients with chronic kidney disease (CKD) can be corrected by the oral or intravenous route. The natural intestinal barrier against iron overload is circumvented by intravenous iron. The balance between benefit and risk of high iron doses remains unclear. In a randomized controlled trial in CKD patients, Agarwal et al. find similar effects of oral and intravenous iron on hemoglobin levels and kidney function decline but more serious cardiovascular events and infections with intravenous iron.