Eculizumab and ravulizumab are anti-C5 monoclonal antibodies that reduce hemolysis, anaemia and thrombotic risk, but are associated with increased risk of infection with encapsulated bacteria, including Neisseria meningitidis. We report a case of life-threatening infection by non-groupable Neisseria meningitidis in a young PNH patient treated with ravulizumab. The gene discussed is C5; the disease is infection.