Pain control during and after any surgical procedure, is extremely essential for the comfort of patients. Pain killers used routinely act by inhibiting cyclooxygenase to control pain and inflammation. Cox-1 is constitutively expressed in most cell types, including platelets, whereas Cox-2 is absent from most healthy tissues but is induced by pro-inflammatory or proliferative stimuli. Cox-1 plays a role in the production of prostaglandins involved in protection of the gastric mucosal layer and thromboxanes (TX) in platelets. Cox-2 generally mediates elevations of prostaglandins associated with inflammation, pain, and pyresis. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen are generally nonselective inhibitors of Coxs. This lack of selectivity has been linked to their propensity to cause gastrointestinal side effects. The new Cox-2 selective inhibitors, or coxibs, show the same anti-inflammatory, analgesic, and antipyretic effects as nonselective NSAIDs but are supposed to have reduced side-effect profiles. This study evaluates whether rofecoxib (50 mg) given one hour pre-operatively or the same drug given one hour post-operatively is more effective in controlling the pain and swelling in mandibular third molar surgery.