We screened patients with chronic respiratory disorders for deep vein thrombosis (DVT) of the lower extremities using ultrasonography. These patients require pulmonary rehabilitation because of their physical disabilities and the reduction in their activities of daily living (ADL). The average soleus vein diameter, which is the reported source of most DVTs, was 6.1±1.5 mm in the control group, 6.8±2.1 mm in the home oxygen therapy (HOT) patients, and 7.0±1.6 mm in the non-HOT patients. The soleus vein diameters in the HOT and non-HOT patients were significantly greater than in the control group (p=0.003). The prevalence of calf DVTs in the HOT patients was significantly higher than in the non-HOT patients (14.3 % vs. 2.0 %, p=0.027). Therefore, patients with chronic respiratory disorders are at greater risks of developing DVT. Furthermore, it appears that not only the deterioration in ADL but also the presence of respiratory disorders and a hypoxic state may influence the onset of DVT in HOT patients. Chronic respiratory disorder is thought to be one of the risk factors for DVT. Therefore, preventive measures, such as ultrasonographic screening examinations, daily living guidance, and physical therapy, are important for patients with chronic respiratory disorders.