Babesiosis is a less common but important tick-borne infectious disease. Over the last 50 years, an increasing number of cases have been reported worldwide, especially in the USA. The northern part of the US is an endemic area where the incidence has risen to 2,000 cases per year in the last decade. Babesia microti, a parasite of small rodents, is the cause of most of these infections in that region. In Europe, 56 autochthonous cases of human babesiosis have been reported since 1957. Most of them were caused by the species Babesia divergens, a parasite of cattle. Since 1992, 13 cases of B. microti infection have been imported from North America into Europe. The disease is serious especially for splenectomised and immunocompromised patients. Although the most important vector of babesiosis in Europe is the tick Ixodes ricinus, infection was transmitted through blood transfusion in number of patients, which can be fatal for immunosuppressed patients. The diagnosis of babesiosis is based on the identification of intraerythrocytic parasites in a blood smear, PCR detection of Babesia DNA, and determination of antibodies by serology and immunofluorescence assays. The disease is treated with antibiotics (azithromycin or clindamycin in a severe course of the disease) and quinine. The increase in human babesiosis is not only due to climate change and tick activity, outdoor leisure activities, and increased human migration, but an important role is also played by improved molecular methods and growing awareness of the disease.