The purpose of this study was to determine mumps virus seropositivity ratio using hemagglutination-inhibiting test in subjects aged between 1 and 18 years. The study was performed on 186 subjects in July 2003. There was seropositivity in Hemagglutination Inhibiting (HAI) antibodies in 178 (95.6%) out of 186 subjects. Seropositivity was 93.6% in the 1-3 age group, 100% in the 4-6 age group, 96.8% in the 7-9 age group, 100% in the 10-12 age group, 92.3% in the 13-15 aged group, and 66.7% in the16-18 age group. Mean titer level was significantly higher (p<0.05) in the 4-6 age group compared to other age groups. As a result, in the Elazığ region, mumps virus seropositivity was found as 95.6% in subjects aged 1-18 years. This result shows that mumps virus infections is acquired in early childhood and that with age HAI antibodies decrease.