Babesiosis or piroplasmosis is a common zoonotic disease among wild and domestic animals. Man can be infected by this hemoprotozoan parasite transmitted by ixodid ticks. More than 400 cases have been observed in the United States, but only 21 cases have been reported in Europe. The American form, caused by B. microti, ranges in severity from asymptomatic to prolonged severe illness. It is characterized by irregular fever and moderate hemolytic anemia. The European form, caused by B. divergens, is a medical emergency with lethality close to 50%, most cases of which are seen in splenectomized patients. The diagnosis requires the identification of the parasite on blood smears (Giemsa). Its morphology is different from that of Plasmodium, but the parasites can be mis-identified, as was the case for the first patient with human babesiosis reported in Switzerland, probably imported from Wales. For clinicians early identification of this disease, which may require renal dialysis and exchange transfusion is essential. The treatment of choice is clindamycin and quinine.