INTRODUCTION: Incidence and risk factors of venous thromboembolism (VTE) are well established in surgical and medical settings, but data in psychiatric units are lacking. The aim of this study was to estimate the incidence of VTE in hospitalized psychiatric patients, and to assess the risk factors for VTE in this specific population. MATERIALS AND METHODS: All consecutive adult patients, admitted for a psychiatric disorder for at least seven days in psychiatric units were considered for inclusion. Patients were evaluated for signs and symptoms of VTE during hospitalization. At Day 10, all participants were interviewed and a systematic compression ultrasonography of the lower limbs was performed. Patients were followed-up until Day 90. RESULTS: Among the 471 included patients, 449 were evaluable at Day 10, and 458 were followed-up until Day 90. Ten deep vein thromboses (DVT) were diagnosed by Day 10 leading to an incidence of VTE of 2.2% (95% CI, 1.1%-4.1%). Six additional symptomatic VTE occurred between Day 10 and Day 90, leading to a 3.5% incidence at Day 90 (95% CI, 2.0%-5.6%). The main factors associated with VTE were age, bed rest, and diagnosis of dementia. The incidence of VTE in patients aged 75 or over with a diagnosis of dementia reached 8.2% at Day 10 and 12.5% at Day 90. CONCLUSIONS: The incidence of VTE in psychiatric units appeared low. However, in older patients, especially those with dementia, the incidence of VTE increased considerably. Further studies are needed to confirm these results.