We report the sonographic findings in 32 patients with malignant disease associated with pleural effusions diagnosed by chest roentgenograms. No tumor lesions were seen in any case on X-ray films. Thoracic sonography, however, detected previously undocumented metastatic disease with diaphragmatic (N = 19), parietal (N = 8), visceral (N = 2) or combined (N = 3) pleural involvement. Additionally, a distinction could be made between nodular lesions (N = 19), sheet-like tumor masses (N = 10), and combined (N = 3) tumor spread. In all cases thoracentesis was performed. Cytology showed malignant cells in 28 patients. Pleural metastasis was histologically confirmed by ultrasound-guided fine needle biopsy in 2 cases. The present study demonstrates the value of scrutinized thoracic sonography in patients with pleural effusion for the detection of pleural metastases.