P arkinson's disease (PD) is a common neurodegenerative disorder that seen in adulthood. Most prevalent symptoms are resting tremor, rigidity, bradykinesia, gait disturbance, and postural abnormalities. The pathogenesis of Parkinson's disease cannot be clearly elucidated. Its proposed that deterioration of dopaminergic neural cells is a multifactorial process. At the present time intracellular-mitochondrial, extracellular and inflammatory/cytokine-related mechanisms are accused of the occurrence of this disease. [1,2] Blood groups first identified in 1900s. Currently there are 36 known blood group systems. Most clinically important are ABO and Rh. Blood group antigens are found on red blood cells, platelets, leukocytes, plasma proteins, certain tissues, and various cell surface enzymes, and also exist in soluble form in body secretions such as breast milk, seminal fluid, saliva, sweat, gastric secretions, urine, and amniotic fluid. [3] ABO blood groups were suggested to be related with several diseases. Disorders related with ABO blood group are infectious disease (cholera, Helicobacter pylori, and Echerichia coli), cardiovascular disease, malignancies and allergic status. [4-6] Introduction: Parkinson's disease is a common neurodegenerative disease that seen in adulthood. Most prevalent symptoms are resting tremor, rigidity, bradykinesia, gait disturbance, and postural abnormalities. Disorders related with ABO blood group are infectious disease (cholera, Helicobacter pylori, and Echerichia coli), cardiovascular disease, malignancies and allergic status. We objectived to elucidate the association between ABO blood group and Parkinson's disease. Methods: We investigated retrospectively the files of 264 adult patients who were diagnosed with Parkinson's disease and had blood type between January 2008 and December 2018 in neurology outpatient clinics included in the study. Results: Distribution of blood groups in patients as follows: