Infection, pulmonary embolism caused by mostly deep venous thrombosis (DVT), hypoxaemia and drugs, used in the treatment of chronic obstructive pulmonary disease (COPD), related arrhythmia, aspiration are mostly responsible for acute exacerbations of COPD. The incidences of DVT and pulmonary embolus were investigated in 56 hospitalised cases with acute exacerbation of COPD. DVT was diagnosed in six (10.7%) cases with coloured doppler ultrasonography (CDU) and in two cases whose examinations were not sufficient enough to diagnose or refuse DVT. Diagnosis of pulmonary embolus was investigated with ventilation/perfusion scintigraphy in eight cases of clinically medium--high-probable pulmonary embolus. Pulmonary embolus was determined in five cases (8.9%). Age, weight, height, disease course, pulmonary function tests, arterial blood gases and haematocrit values of the cases did not predict the diagnosis of DVT and pulmonary embolus in our cases.