The seroprevalence and risk factors for infection with hepatitis E virus (HEV) were analysed in five regions of Turkey, where one-third of acute hepatitis cases are non-A, non-B. Antibodies to HEV (anti-HEV) were found in 80 (5.9%) of 1350 subjects. Independent predictors of anti-HEV were age over 25 years, less than elementary education, antibodies to hepatitis C virus, and residence in the warmest region (Adana). Whereas none of 105 subjects in the second decade of life were HEV seropositive, 17 (3.7%) of 464 and 28 (9.1%) of 308 of those in the third and fourth decades of life, respectively, had anti-HEV (p < 0.001). These data demonstrate that in Turkey HEV is more prevalent in warmer regions and in adults, beginning in the third decade of life.