The link between coagulation system disorders and COVID-19 has not yet been fully elucidated . With the aim of evaluating the association of several coagulation proteins with COVID-19 severity and mortality, we performed a cross-sectional study in 134 patients classified according to the highest disease severity reached during the disease . We found higher levels of antithrombin, prothrombin, factor XI, factor XII and factor XIII in asymptomatic/mild and moderate COVID-19 patients than healthy individuals . Interestingly, decreased levels of antithrombin, factor XI, XII and XIII were observed in those patients who eventually developed severe illness . Additionally, survival models showed us that patients with lower levels of these coagulation proteins had an increased risk of death . In conclusion, COVID-19 provokes early increments of some specific coagulation proteins in most patients . However, lower levels of these proteins at diagnosis might 'paradoxically' imply a higher risk of progression to severe disease and COVID-19-related mortality.