Background and aim: To establish an appropriate dental preventive program, relevant data should be collected from all over the country. The aim of the present study was to find out the care index, Treatment needs and DMFT score and its related factors in 12 year – old male and females students studying in Karaj middle schools in 2004.materials and methods: The study was designed as a cross sectional surrey in 4 educational districts of Karaj on 768 students. Study samples were chosen through multi stage random sampling from public and private schools. The questionnaire and study forms were filled through inter view with students and their dental examination. All the examinations were carried out in a well – lit classroom with sterile packed instruments, mask and glove DMFT was calculated by the WHO criteria Some of the related factors were frequency of dental examination, the number ofthe students siblings, mouth breathing, socio economic status of the family the prevalence at problem in samples established and confidence in terval in society was estimated. The role of the related factors was statistically analyzed with chi squarettest.Results: Total samples were 768 people (384 male and 384 female). DMFT was 2.67±2.2 in girls and 3.59±2.59 in boys. Treatment needs and care index was %85/74 and %11/8 in girls and %93.54 and%5.94 in boys respectively.%21.9 girls and%13.55 boys were caries free in this study mothers occupation (P<0/03 in girls and P<0/005 in boys), birth rank (P<0/025 in boys), mouth breathing (p< 0/025), frequency of dental examination (P<0/008 in girls), were significantly related to DMFT. In girls a significant relation ship was found between the type of school and DMFT (P<0/0011).Conclusions: DMFT score was high er than WHO goals specially in boys and education in preventive and Treatment fields is recommended. Also, more re search is recommended in the related factors field.