An important milestone in the history of blood transfusion was the discovery of the ABO blood groups by Karl Landsteiner, followed by discovery of Rh (D) antigen. Landsteiner’s achievements lead to several discoveries in the field of immunohaematology. The ABO blood group is useful in selecting the appropriately matched blood group during blood transfusion, organ transplantation, finding out association of blood groups and diseases etc. ABO blood group system classifies blood groups of people into four different types namely A, B, O and AB. The need for the study of frequency distribution of blood group is multipurpose. This study was done to know the frequency distribution of blood groups among first year medical students. This study was conducted on 100 medical students in the Department of Physiology at CAIMS medical college in Karimnagar Telangana state. The blood samples were collected by finger prick method. ABO blood grouping and Rhesus factors (Rh) typing determined by glass slide method. Out of total 100 medical students who volunteered, 30 were males and 70 females. In our study, the most frequently occurring blood group was O ( 42%) followed by B group (29%), A group 17% ) and AB group(12% ) . 81% students were Rh positive whereas only 19% were Rh negative. This study may enable us to contact individuals belonging to a particular blood group at times of medical emergencies when blood transfusion is required.