Background: Acutely ill medical patients experience deep venous thrombosis (DVT) during the hospitalization, however the time course of DVT is still unclear. Objectives: To evaluate risk factors in acutely ill hospitalized medical patients for asymptomatic DVT (ADVT) and symptomatic DVT (SDVT) within 48 hours from admission and at discharge and comparing prophylaxis treatment with (group A) and without (group B) low-molecular weight heparin (LMWH) Patients/Methods: Consecutive acutely ill medical patients underwent duplex color compression ultrasonography (CUS) of proximal lower limb veins within 48 hours from admission and at discharge to screen for ADVT and to document SDVT. Primary end-point of the multicentric study was the incidence of all DVT. Biographical characteristics at hospitalization, D-Dimer and DD-improve score at entry and at discharge were analyzed by univariate and multivariate analysis to identify variables associated with DVT and compared between groups.Results: Of 2,100 patients (1002 females, 998 males, age 71±16) included 58 (2.7%) (31 females. 27 males, age 77±14) had ADVT at admission. A binary logistic regression analysis showed that age (O.R.: 1.03, 95% C.I. 1.007-1.05, p=0.008), thrombophilia (O.R.: 10,95% C.I. 3-34, pConclusions: The incidence of ADVT and of SDVT was high (3%) upon admission of acutely ill medical patients upon hospitalization. Advanced age, active cancer, thrombophilia, elevated D-dimer and IMPROVE-DD score greater than 2.5 were risk factors for ADVT should analyzed upon hospitalization for decision of treatment with LMWH. The benefit of therapeutic dose of anticoagulation needs to be investigated in patients with ADVT and specific risk factors. Trial registration: NCT03157843