Chicken pox highly contagious and common throughout the world, is an infectious disease caused by varicella zoster virus (VZV). This study was conducted to determine the seroprevalence of VZV in a population under age 30 and to identify the relationship of VZV seroprevalence and several characteristics of the study subjects in nine provinces of Turkey. The sampling method of 30 clusters recommended for field studies was used for selecting subjects of a pre-determined number in the rural and urban areas in each province. For this, a total of 60 groups, 30 clusters in the rural and 30 in the urban areas were determined. It was planned that a total of 4800 subjects, including 600 subjects from five big provinces (Istanbul, Ankara, Izmir, Adana, Diyarbakir) and 450 subjects from the remaining smaller provinces (Samsun, Erzurum, Trabzon, Edirne), be included in the study. ELISA method was used to examine the blood samples for VZV seropositivity. Positive VZV seroprevalence was detected in 77.8% of 4387 subjects under age 30 in nine provinces of Turkey. There was no difference in seroprevalence rate between rural and urban areas. Seroprevalence was found to be 79.0% in urban areas and 76.3% in rural areas. Seroprevalence increased with age. Seroprevalence was 20% at the age of 1 year, subsequently increased to 40% at the age of 4 years, 60% at the age 6 years, 80% at the age of 8 years, 85% at the age of 10 years, and then remained at 85-90% in subjects over the age of 10 years. In order to develop vaccination protocols and take appropriate preventive health care measures against diseases in different countries, it is very important to know the seroprevalence of any disease for an individual country. (C) 2002 Elsevier Science Ltd. All rights reserved.