Symptomatic pericardial effusion in lung cancer patients: the role of fluid cytology. During the years 1975-1988, twenty lung cancer patients with symptomatic pericardial effusion were treated conservatively at our center. Echocardiography demonstrated small pericardial effusion in 2 patients, medium size effusion in 3 patients and large amount of fluid in 15 patients. Fifteen patients developed cardiac tamponade; in three of these patients, this was the presenting manifestation of lung cancer. Pericardiocentesis resulted in prompt, though temporary, symptomatic relief in all patients. Fluid cytology demonstrated suspected malignant cells in 2 patients and malignant cells in 13 patients. Based on cytology, the diagnosis of adenocarcinoma was established in six patients, small cell carcinoma in three patients, and epidermoid carcinoma in one patient. All patients were dead within 9 months from the time of diagnosis of pericardial effusion; 17 died within less than 3 months. It is concluded that pericardial effusion in lung cancer is indicative of rapid tumor progression and short survival. Fluid cytology provides an immediate and accurate means of diagnosis. 