Objective: The aim of this study is to evaluate the effect of blood groups (BGs) on Covid-19 contraction and prognosis and to reveal the coefficients. Methods: Patients who referred to Covid-19 outpatient clinics and had an established diagnosis of Covid-19 were included in the study. Their BGs, previous diagnoses and blood examination findings were retrospectively analyzed. Duration of hospitalization, clinical course and survival were recorded. Results: The mean age of 365 subjects, 210 female and 155 male, was 45.5 years. Subjects with BG A developed Covid-19 at significantly higher rates (p = 0.001), while BG O was found associated with lower rates (p = 0.005). Lymphocyte count was found lower (p = 0.035) and rate of lung parenchymal involvement was higher (p = 0.003) in patients with Rh antigen. It was found that a higher percentage of patients with B BG required treatment in the intensive care unit (ICU) compared to other ABO BGs (p = 0.015). Conclusion: These results suggest a higher risk of Covid-19 contraction in the population with BG A and lower risk for BG O population while indicating poorer prognosis for patients with BG B.