Thrombocytopenia, fever, and acute renal failure are characteristic features of nephropathia epidemica, the predominant hantavirus infection in Europe. However, clinical presentation and blood cell counts may point to other disorders, such as a hematologic disease, particularly when impairment of renal function is not evident. This differential diagnosis often results in further extensive and unnecessary testing. We describe 3 patients with hantavirus infection with no renal failure, in whom a hematologic disorder was initially suspected. Serologic testing of hantavirus finally unraveled the mystery, and outcome of the patients was excellent. It is conceivable that similar cases often remain undiagnosed. Thus, testing for hantavirus should always be considered in cases of thrombocytopenia and fever of unknown origin, especially in areas endemic for the infection.