Cold agglutinin disease is a very rare haemolytic anaemia characterized by antibody-mediated haemolysis, complement activation, thrombosis and poor quality of life. In recent years, our understanding of the complement system and its role in disease has increased dramatically. However, because there is an increased risk of infection with inhibiting complement at the complement 5 and complement 3 levels, blocking the classical complement pathway is being explored instead as a way to strategically inhibit the complement system while minimizing the infection risks. Sutimlimab is a humanized immunoglobulin G4 antibody developed to inhibit the classical complement pathway. Its role and efficacy in treating patients with cold agglutinin disease will be the focus of this paper.