Severe haemolysis is a rare, but potentially life-threatening, complication of cytomegalovirus (CMV) infection in immunocompetent adults. Treatment with steroids or immunoglobulins, or even splenectomy, may be justified when an autoimmune mechanism can be identified as the cause of the anaemia. Described here is the case of a previously healthy patient who presented with severe haemolytic anaemia following CMV infection. The patient's haemoglobin level fell to 5.1 g/dl while extensive testing for an autoimmune mechanism remained negative. The patient made a slow but full recovery without additional medication or blood transfusions. This case demonstrates that severe haemolytic anaemia following CMV infection is possible even when presently available tests fail to show autoimmune positivity. In immunocompetent subjects a wait and see policy, with supportive care when necessary, is likely to be justified.