Critically ill patients with COVID-19 pneumonia suffered both high thrombotic and bleeding risk. The effect of SARS-CoV-2 on coagulation and fibrinolysis is not well known. We conducted a retrospective study of critically ill patients admitted to an intensive care unit (ICU) a cause of severe COVID-19 pneumonia and we evaluated coagulation function using rotational thromboelastometry (ROTEM) on day of admission (T0) and 5 (T5) and 10 (T10) days after admission to ICU. Coagulation standard parameters were also evaluated. Forty patients were enrolled into the study. The ICU and the hospital mortality were 10% and 12.5%, respectively. On ICU admission, prothrombin time was slightly reduced and it increased significantly at T10 (T0 = 65.1 +/- 9.8 vs T10 = 85.7 +/- 1.5, p = 0.002), while activated partial thromboplastin time and fibrinogen values were higher at T0 than T10 (32.2 +/- 2.9 vs 27.2 +/- 2.1, p = 0.017 and 895.1 +/- 110 vs 332.5 +/- 50, p = 0.002, respectively); moreover, whole blood thromboelastometry profiles were consistent with hypercoagulability characterized by an acceleration of the propagation phase of blood clot formation [i.e., CFT below the lower limit in INTEM 16/40 patients (40%) and EXTEM 20/40 patients (50%)] and significant higher clot strength [MCF above the upper limit in INTEM 20/40 patients (50%), in EXTEM 28/40 patients (70%) and in FIBTEM 29/40 patients (72.5%)]; however, this hypercoagulable state persists in the first five days, but it decreases ten day after, without returning to normal values. No sign of secondary hyperfibrinolysis or sepsis induced coagulopathy (SIC) were found during the study period. In six patients (15%) a deep vein thrombosis and in 2 patients (5%) a thromboembolic event, were found; 12 patients (30%) had a catheter-related thrombosis. ROTEM analysis confirms that patients with severe COVID-19 pneumonia had a hypercoagulation state that persisted over time.