Human granulocytic ehrlichiosis is an emerging infectious disease, which is transmitted by the tick Ixodes ricinus in Europe, like other diseases: Lyme disease, tick-borne encephalitis, babesiosis... This tick lives in the forest and its hematophagic activity ranges from April to October. Flu and febrile symptoms ten days after tick bite should suggest diagnosing the disease. Disease evolution is generally favorable, even if serious complications may occur. Leukopenia, thrombocytopenia, and elevated serum transaminases are common laboratory findings. Complementary assays useful for the diagnosis are: blood smear, indirect immunofluorescence, and polymerase chain reaction. Biological diagnostic criteria are more and more accurate, with the evolution of knowledge and technique. Tetracycline treatment generally leads to clinical and biological recovery. Informing physicians and occupationally exposed people should reinforce current prevention measures against tick bites.