Background: In this study, the body mass index (BMI) of Turkish population is calculated using a sample of 4205 persons consisting of 2263 male and 1942 female individuals in 2007. The study contains data from all seven geographical regions (Aegean, Black Sea, Central Anatolia, Eastern Anatolia, Marmara, Mediterranean and Southeast Anatolia) of Turkey and from all age groups from 20 to 85 years. Method: In this study, height and weight data were measured and used for calculating the BMI of Turkish population accounting for age and regional effects. Results: This study's analysis found that age, region and gender are significant determinants on obesity of Turkish population. Also, Turkish population has higher obesity prevalence than most of the European countries. Overall, it was found that 56% of Turkish Population is overweight while 41% is in the normal range. Conclusions: This is the first study related to obesity in Turkey covering all seven regions and all age groups. Analyzing the differences of obesity prevalence between genders, geographical regions and age groups will be beneficial for better understanding the reasons behind obesity in Turkey.