Both obesity and type 2 diabetes (T2D) are recognized risk factors for developing a more severe form of COVID-19, with a higher death rate. Metformin is considered as the first-line medication for the treatment of T2D, especially in obese patients. Beyond its glucose-lowering activity, metformin exerts pleiotropic effects, among which an anti-inflammatory effect that could be beneficial. However, metformin is contraindicated in case of severe renal insufficiency, liver failure and/or unstable heart failure, because of a risk of lactic acidosis. Yet, COVID-19, besides the well-known pneumonia that can be responsible for severe hypoxemia, may be associated with multisystemic organ failure, among which kidneys, liver and heart. Thus, the question arises whether metformin, which represents the background therapy in above 80 % of patients with T2D, should be continued in patients exposed to SARS-CoV-2 or instead be stopped. This article summarizes the most important results of observational studies, which all argue for a beneficial effect of metformin therapy that is associated with a significant reduction in mortality among hospitalized patients with T2D due to COVID-19. Finally, some practical advices will be given.