BACKGROUND Periodontal diseases are very prevalent among large populations worldwide. They have multi-factorial aetiology. Some researchers have concluded that these diseases have genetic predisposition along with other systemic diseases. However, if such a relationship between blood groups and periodontal disease can be established beyond a reasonable doubt, it can be concluded that the presence of particular blood group antigen has somehow increased the susceptibility to the disease. The present study was planned to be conducted on two major ethnic groups of Indian population to correlate the relationship between chronic periodontitis and ABO blood groups. METHODS A cross-sectional study was conducted among 500 systemically healthy patients with chronic periodontitis who were randomly selected from the two major ethnic groups of Indian population, in the age group of 25 years to 75 years of both the sexes. Each group had 250 patients. Group I: 250 North Indian (NI) patients with Chronic Periodontitis; Group II: 250 South Indian (SI) patients with Chronic Periodontitis. Both the population groups were divided into five age groups: a. 25-35 years, b. 36-45 year's c. 46-55 years, d. 56-65 years, e. 66-75 years. Their blood samples were taken through finger prick method to analyse ABO blood groups and Rh factor. The obtained data was analysed for frequency distribution and statistical significance. RESULTS It was observed that in both the population groups, maximum individuals having chronic periodontitis belonged to B+ blood group, which was followed by O+>A+>AB+. There was very less prevalence of Rh-negative blood group patients in both the population groups. CONCLUSIONS Individuals having B+ blood group are more likely to have chronic periodontitis followed by O+>A+>AB+.