We retrospectively collected data from patients enrolled between 1996 and 1997, to evaluate the efficacy of sono-guided pig-tail-catheter drainage in cancer patients with large, symptomatic, amounts of malignant effusion and to evaluate the hemodynamic change after effusion drainage. A total of 477 pig-tail catheter drainage procedures were performed on 342 cancer patients. Sonographic findings, volume drained within 36 h after pig-tail insertion, heart rate and respiratory rate 24 h before and after drainage, and dyspnea sensations were recorded. We found that unilateral right-side effusion was the most frequent presentation. The mean amount of effusion drained within 36 h was 1,747 ml in cancer patients. The decreases in heart rate (from 97/min to 91/min) and in respiratory rate (from 23/min to 21/min) were both statistically significant. There was no significant correlation between the amount of effusion before drainage and the heart rate or respiratory rate. The amount drained within 36 h was correlated significantly with the changes in heart and respiratory rates. Dyspnea sensations decreased or subsided in 91% of the patients within this time period. There were few complications with the pig-tail drainage procedure. Sono-guided pig-tail drainage is a safe and convenient method of effusion drainage in cancer patients. It not only provides temporary relief of symptoms from massive pleural effusions, but can also be used for pleurodesis if needed.