caries free prevalence among 6, 12 & 15- year old school children in kerman during 2000-2005

background: dental caries is the most infective microbial dental disease. basic screening survey is an epidemiologic index for determination of caries prevalence. the aim of this study was assessment of caries free prevalence in 6, 12 & 15- year old school children in kerman during 5 years.   methods: in this cross-sectional, descriptive –analytic study, 15369 school children aged 6, 12 &15 years old were selected by multistage sampling method. data collection was done through clinical examination and a questionnaire. clinical examination was performed with use of the ball-point explorer and dentistry mirror. the questionnaire included the age, sex, parent's educational level, tooth brushing and dental visit frequency. data were analyzed by t and χ 2 tests.   results: mean caries free prevalence in female and male subjects were respectively 17.8% and 15.6% (in 6 year old group), 24.5% and 24.1% (in 12 year old group) and 21.5% and 25.3% (in 15 year old group). there was a statistically significant relationship between caries free prevalence and age so that, in 6 year-old student's caries free was more prevalent than other age groups. conclusion: the caries free index in 6, 12 & 15- year old school children of kerman was lower than who standards.