Blood plasma is a large reservoir of circulating mediators of inflammation and its expansion has been associated with unfavorable outcomes in patients with inflammatory and cardiovascular diseases. The aim of this study was to determine clinical and prognostic value of estimated plasma volume status (ePVS) in hospitalized patients with COVID-19. We retrospectively investigated 5871 consecutive COVID-19 patient hospitalized in our tertiary-level institution in period 3/2020-6/2021. ePVS was determined using the Strauss-derived Duarte formula and was correlated with clinical characteristics and unwanted outcomes. Median ePVS was 4.77 dl/g with interquartile range 4.11–5.74. Higher ePVS was significantly associated with older age, female sex, higher comorbidity burden, worse functional status, less severe COVID-19 clinical presentation with lower severity and longer duration of symptoms, but more pronounced inflammatory profile with higher C-reactive protein, interleukin-6 and D-dimer levels (P < 0.05 for all analyses). In the multivariate regression analysis U shaped relationship of ePVS with mortality was revealed, present independently of age, sex, COVID-19 severity and comorbidity burden. In addition, higher ePVS was independently associated with higher tendency for mechanical ventilation, intensive care unit treatment, venous thromboembolism, major bleeding and bacteriemia and lower ePVS was independently associated with tendency for arterial thrombotic events. Higher ePVS, indicative of plasma volume expansion and inflammatory cytokine accumulation, may predispose respiratory deterioration and venous thromboembolism, despite less severe initial clinical presentation. Lower ePVS, indicative of hemoconcentration, may predispose arterial thrombotic events. Both may be associated with higher mortality in hospitalized COVID-19 patients.