OBJECTIVE: To review the impact of epidural vs systemic analgesia on postoperative pulmonary complications. DATA SOURCES: Search of databases (1966 to March 2006) and bibliographies. STUDY SELECTION: Inclusion criteria were randomized comparison of epidural vs systemic analgesia lasting 24 hours or longer postoperatively and reporting of pulmonary complications, lung function, or gas exchange. Fifty-eight trials (5904 patients) were included. DATA EXTRACTION: Articles were reviewed and data extracted. Data were combined using fixed-effect and random-effects models. DATA SYNTHESIS: The odds of pneumonia were decreased with epidural analgesia (odds ratio [OR], 0.54; 95% confidence interval [CI], 0.43-0.68), independent of site of surgery or catheter insertion, duration of analgesia, or regimen. The effect was weaker in trials that used patient-controlled analgesia in controls (OR, 0.64; 95% CI, 0.49-0.83) compared with trials that did not (OR, 0.30; 95% CI, 0.18-0.49) and in larger studies (OR, 0.62; 95% CI, 0.47-0.81) compared with smaller studies (OR, 0.37; 95% CI, 0.23-0.58). From 1971-2006, the incidence of pneumonia with epidural analgesia remained about 8% but decreased from 34% to 12% with systemic analgesia (P <.001); consequently, the relative benefit of epidural analgesia decreased also. Epidural analgesia reduced the need for prolonged ventilation or reintubation, improved lung function and blood oxygenation, and increased the risk of hypotension, urinary retention, and pruritus. Technical failures occurred in 7%. CONCLUSION: Epidural analgesia protects against pneumonia following abdominal or thoracic surgery, although this beneficial effect has lessened over the last 35 years because of a decrease in the baseline risk.