Background : The management of thoracic empyema and complicated parapneumonic effusion requires adequate antibiotics use and prompt drainage of infected pleural space. Tube thoracostomy for loculated empyema has low success rate and is also an invasive procedure with potential morbidity. Complications include hemothorax, perforation of intra-abdominal or intra-thoracic organs, diaphragmatic laceration, empyema, pulmonary edema, and Horner's syndrome. Given the potential morbidity of traditional chest tube insertion, use of the image-guided pigtail catheter drainage(PCD) of empyema has been employed. We retrospectively analyzed the medical records of patients with empyema or complicated parapneumonic effusion to determine the efficacy of percutaneous pigtail catheter drainage. Materials and Methods : 45 patients with complicated parapneumonic effusions or empyema were treated at Gil medical center from January 1998 to June, 1999. All were initially given PCD procedure and the following data were collected: clinical symptoms at the time of diagnosis, alcohol and smoking history, the characteristics of pleural effusion, radiologic findings (at the time of catheter insertion, removal and 1 month after catheter removal), the amount of effusion drained for initial 24 hours, the time from catheter insertion to removal and the use of surgical approach. Results : Male gender was more frequent (42 men vs. 3 women), the mean age of the study population was 52(range: 21~74) years. Empyema was found in 23 patients, complicated parapneumonic effusion in 22 patients. Four patients(three, parapneumonic effusion and one, with empyema) with PCD only treated, were cast off. Among the available patients, 36(80%) patients were treated with PCD only or PCD with urokinase. Among the 23 patients with empyema, surgical approach was required in five patients(27.1%, one required decortication, four open thoracostomy), one patient, treated with surgical procedure, died of sepsis. There was no significant difference of the duration of catheter insertion, the duration of hospital admission after catheter insertion and the mean amount of effusion drained for initial 24 hours between the patients with only PCD treated and the patients treated with PCD and urokinase. The duration of catheter insertion($9.4{\pm}5.25days$ vs. $19.2{\pm}9.42days$, p<0.05) and the duration of hospital admission after catheter insertion($15.9{\pm}10.45days$ vs. $38.6{\pm}11.46days$, p<0.01) of the patients with only PCD treated were more longer than those of the patients treated with surgical procedure after PCD. They were same between the patients treated with urokinase after PCD and the patients treated with surgical procedure after PCD($11.1{\pm}7.35days$ vs. $19.2{\pm}9.42days$, p<0.05, $17.5{\pm}9.17days$ vs. $38.6{\pm}11.46days$, p<0.01). In 16 patients(44.4%) with only PCD treated or PCD and urokinase treated, the amount of effusion at the time of catheter removal was decreased more than 75% and in 17 patients(47.2%) effusion decreased 50~75%. .In one patient effusion decreased 25~50%, in two patients effusion decreased less than 25%. One month after catheter removal, in 35 patients(97.2%, four patients were cast off), the amount of pleural effusion was successfully decreased more than 50%. There were no complications related to pigtail catheter insertion. Conclusion : In this study, PCD seemed to be an early efficacious procedure in treating the patients with complicated parapneumonic effusion or empyema without any serious procedure related complication.