Methodology: This observational study covered the period July 2005 ???? July 2006. We included patients 18 years old and above who underwent thoracentesis for a pleural effusion documented by an upright chest radiograph. The primary outcome was the occurrence of pneumothorax after thoracentesis. Data on potential patient-related and procedure-related risk factors for pneumothorax were also collected. Results: Fifty-seven patients with pleural effusion were included and they underwent a total of 62 thoracenteses. There were 3 incidents of pneumothorax, with a rate of 4.8% (Binomial exact 95% CI 1.0 - 13.5%). No associations can be made between patient-related and procedure-related risk factors and the occurrence of pneumothorax after thoracentesis because of the very small number of episodes of pneumothorax in this study. Conclusion: Thoracentesis is a low-risk procedure performed in a patient with pleural effusion, either for diagnostic or therapeutic indications or both.