We describe a patient with severe symptomatic thrombocytopenia and haemolytic anaemia caused by cytomegalovirus (CMV) infection. As far as we know, this is the second case in the literature. Treatment with ganciclovir seemed to be more effective for thrombocytopenia than treatment with corticosteroids. The hypothetical mechanisms leading to thrombocytopenia and haemolysis in CMV infection are briefly discussed. In cases of acute thrombocytopenia and clinical manifestations of an infectious disease, with or without haemolysis, testing for CMV may be useful in connection with therapeutic consequences.