Objective: Nonsteroidal anti-inflammatory drugs inhibit platelet aggregation and increase bleeding time; however, they are required to control pain and swelling following dental surgery. The objective of this study was to evaluate possible changes on blood coagulation tests by using ketoprofen and diclofenac potassium after removal of mandibular third molars. Method and Materials: Fifty-one subjects between 16 and 30 years old, with no history of gastrointestinal disorders or allergy to anti-inflammatory components, were randomly assigned to 2 groups: 27 patients received 50 mg of ketoprofen, and 24 patients received 25 mg of diclofenac potassium. Subjects started the oral medication 2 hours before surgery and continued taking it every 8 hours for 5 days. Blood samples were collected preoperatively and on the final day of the drug regime to evaluate prothrombin time, activated partial thromboplastin time, clot retraction, and platelet count. Results: Student t test for matched pairs did not show a significant difference between pre- and posttreatment variables for both antiinflammatory drugs. Conclusion: These results suggest that the safety of ketoprofen and diclofenac potassium is comparable to their anticoagulation effect. Palabras clave: blood-coagulation tests, nonsteroidal anti-inflammatory agents, third molar, tooth extraction