Background & Objective: Control of TB is regarded as a health priority program in underdeveloped countries, and Iran in no exception in this regard. Annual risk of infection (ARI) is an important index in this program. This index shows the percentage of people in a society who have been contaminated, and consequently their skin test has changed from negative to positive. In this study, Tuberculin skin test is conducted on Ardabil primary school students and its changes, if any, after one year have been regarded using renewed skin test in order to show ARI in this age group.

 Methods: 780 students were selected from among 17 primary schools using simple random sampling method. They were 8-14 years old, (mean 9.92). Tuberculin skin test was performed on all subjects two times with a one- year interval (May 1998-1999). The test results were recorded and analyzed. In this study PPD over 10 mm was considered positive.

 Results: In 55 (7.1%) students the test was positive in both tests, and in 33 (4.2%) students, PPD changed from negative (first time) to positive (second time) and in 78 subjects the results were doubtful. 765 students (98.1%) had history of BCG vaccination.

 Conclusions: This study indicated that, firstly, over the time, BCG has little effect on Tuberculin skin test, and secondly, the high rate of tuberculin skin test changes from negative (first time) to positive (second time) represents probability of severe contamination in this area.