Acute exacerbation of chronic obstructive pulmonary disease (COPD) is associated with dyspnea and, consequently, reduced mobility. Immobility is a recognized risk factor of deep-vein thrombosis (DVT), but few data exist regarding the prevalence of DVT in patients with acute exacerbation of COPD. Real-time B-mode ultrasonography (US) is a noninvasive screening method for the diagnosis of DVT. We therefore used US to investigate the prevalence of DVT in patients with an acute exacerbation of COPD. In a prospective cohort study, 196 patients with COPD were studied [110 males, 86 females, age: 66.9 +/- 9.1 years, weight: 63.5 +/- 12.7 kg, forced expiratory volume in 1 s (FEV1): 0.7 +/- 0.2 liters, and a ratio of FEV1 to vital capacity (VC): 37 +/- 6%] in a respiratory intensive care unit on the day of admission. Patients with reduced mobility due to other disease were excluded. All US were performed by one experienced person with a 5-MHz linear scanner. The views of the lower extremity were subdivided into three segments: (1) the common femoral, (2) superficial femoral veins including the long saphenous vein and (3) the popliteal vein. In 21 of 196 COPD patients (10.7%), DVT were demonstrated; 18 of these were asymptomatic. Bilateral DVT were not found. In 6 patients, additional diagnoses were: Baker's cyst (n = 3), inguinal lymph node (n = 1) and knee joint effusion (n = 2). There were no differences between patients with and with DVT with respect to age, hemoglobin, PO2, PCO2, pH, FEV1, VC or dyspnea scale. DVT in the lower extremity, which was not detectable on clinical examination, was relatively common in patients with an acute exacerbation of COPD. All clinical variables measured (age, weight, dyspnea scale, lung function, hemoglobin, hematocrit and blood gases) failed to predict patients more likely to have DVT.