Post-operative pain relief is of paramount importance not only for humanitarian reasons but also for a better recovery course. We investigated the effect of thoracic epidural analgesia, lumbar epidural analgesia and conventional intra-muscular pethidine on sixty morbidly obese patients undergoing renal surgery regarding perioperative lung volumes measured by spirometry, patients’ oxygenation detected in arterial blood gases analysis & post-operative pulmonary complications screened by chest imaging. We also compared thoracic versus lumbar epidural analgesia concerning total drug requirements & undesirable effects on patients’ blood pressure and heart rate. We found that the use of epidural analgesia, particularly thoracic, was associated with a better outcome.