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One thousand orthopedic procedures in 924 patients given spinal or epidural anesthesia were prospectively studied to determine the risk of hemorrhagic complications associated with regional anesthesia. A history of excessive bruising or bleeding was elicited in 115 (12%) patients. Preoperative antiplatelet medications were taken by 386 (39%) patients. Aspirin was the most frequently reported antiplatelet drug and was taken by 193 patients. Subcutaneous heparin was administered to 22 patients before surgery on the operative day. One patient of 774 tested had a preoperative platelet count less than 100,000/mm3. In addition, 26 of 171 preoperative prothrombin times and 10 of 115 preoperative activated partial thromboplastin times were longer than normal. Only 31 preoperative bleeding times were performed; five were prolonged. There were no documented spinal hematomas (major hemorrhagic complications). Blood was noted during needle or catheter placement (minor hemorrhagic complication) in 223 (22%) patients, including 73 patients with frank blood in the needle or catheter. Preoperative antiplatelet therapy did not increase the incidence of minor hemorrhagic complications. However, female gender, increased age, a history of excessive bruising/bleeding, surgery to the hip, continuous catheter anesthetic technique, large needle gauge, multiple needle passes, and moderate or difficult needle placement were all significant risk factors. The lack of correlation between antiplatelet medications and bloody needle or catheter placement (producing clinically insignificant collections of blood in the spinal canal or epidural space) is strong evidence that preoperative antiplatelet therapy is not a significant risk factor for the development of neurologic dysfunction from spinal hematoma in patients who undergo spinal or epidural anesthesia while receiving these medications.