For reasons unknown, metastatic squamous-cell carcinoma is a rare cause of pleural effusions and is even less common in pericardial effusions. A review of all pericardial effusions examined in the Cytology Service at Montefiore Medical Center over a 15-year (1980-1994) period was undertaken (N = 251). Four cases with metastatic squamous-cell carcinoma were identified among 39 malignant effusions. Two patients with metastatic squamous-cell carcinoma presented with cardiac tamponade, and the other two cases had progressive cardiac failure. The diagnostic cells on cytology evaluation were scant in all four cases but exhibited classical features of metastatic squamous carcinoma, such as cytoplasmic keratinization, intercellular bridges, and occasional "pearl" formation. Pericardial biopsies available in three patients, two with cardiac failure and one with cardiac tamponade, were negative. In all four cases the primary tumor was a bronchogenic carcinoma. Metastatic squamous-cell carcinoma is an uncommon cause of pericardial effusion and usually indicates the presence of a bronchogenic carcinoma with a rapidly fatal outcome. Cytologic examination of pericardial fluid is essential in the evaluation of such patients.