Each y a few cases of TBE infection are described in Alsace, France which lies at the occidental limit of the endemic zone of tick-borne encephalitis (TBE). Hence we carried out a retrospective epidemiological and clinical study of TBE infection in Alsace. Data were collected from serological results sent to the Institut de Virologie (Université Louis Pasteur) in Strasbourg. All samples positive for specific IgM against TBE were retained. The physician in charge of each patient was asked to provide clinical, epidemiological and biological data and with his agreement the medical file was referred to us. Since 1968, 64 cases of TBE infection, occurring between April and November, had been described. In 56% of cases, flu-like symptoms preceded neurological symptoms. Most patients had meningitis (54%) or meningoencephalitis (34%). There was no death due to TBE. Two areas were more highly endemic for the disease: the Guebwiller valley in low mountain country and the Neuhof forest, near Strasbourg in the plain of Alsace. In the last 2 y of the study, a third zone seemed to emerge, in the Munster valley. This epidemiological survey revealed the existence in Alsace of 2 endemic zones of TBE with a third zone possibly emerging in the last few y. The survey must be continued to follow the evolution of the disease.