The synthesis of erythropoiesis-stimulating agents (ESAs), especially recombinant human erythropoietin, has provided a new therapeutic option for the treatment of patients with various forms of anemia, including that of chronic renal disease, malignancy, hematologic disorders, prematurity, and acquired immune deficiency syndrome. These agents are effective in improving the hematologic response and reducing the need for red blood cells transfusion, and they also appear to have a positive effect on some health-related quality-of-life indicators. The incidence of side effects and survival, however, remains highly uncertain, and several studies have recently highlighted the problem of an increased trend of tumor progression, mortality and thrombotic complications, especially venous thromboembolism, in patients undergoing therapy with ESAs. Specifically, the biological background underlying the prothrombotic effects of ESAs is multifaceted (polycythemia/hyperviscosity syndrome, hypertension, thrombocytosis, platelet hyperactivity, activation of blood coagulation) and context dependent, and it most likely requires the presence of additional prothrombotic factors. Nevertheless, this clinical and biological evidence supports the hypothesis that therapy with ESAs might not be ultimately beneficial or advantageous in patients with anemia of chronic disorders, and these drugs should not be routinely used as an alternative to blood transfusion unless future studies affirm safety and clinical benefits within these populations.