Two hundred and ten patients with exudative pleural effusion were studied by ultrasound for sonographic signs of pleural carcinomatosis. Images were evaluated for echoes within the fluid, septations, sheet-like or nodular pleural masses, and associated lesions of the lung. Our results showed that sonographic findings of echogenic or septated fluid were unspecific for malignancy. Only the evidence of pleural masses was characteristic of malignant effusion. Ultrasound of the chest should therefore be carried out before invasive diagnostic procedures are planned.