Background and objectivesIn the pandemic caused by SARS-CoV-2, identifying which risk factors are associated with the most serious forms of the disease is important. Blood group A has been presented in various studies as a poor prognostic factor. The objective of this study was to evaluate whether patients with blood group A were associated with more important comorbidities, measured by the Charlson Index, which may explain their worse clinical evolution. Patients and methodsA prospective and consecutive study examined 100 patients diagnosed with COVID-19 and admitted in March 2020. A multivariate linear regression model was used to evaluate the association of blood group A with the Charlson Index. ResultsPatients in group A had a higher Charlson Index (P = .037), rate of lymphopenia (P = .039) and thrombopenia (P = .014), and hospital mortality (P = .044). Blood group A was an independent factor associated with the Charlson Index (B 0.582, 95% CI 0.02-1.14, P = .041). ConclusionsGroup A was independently associated with greater comorbidity, associated with an increase of 0.582 points in the Charlson Index compared to other blood groups. It was also associated with lower hospital mortality.