A total of 290 consecutive patients who underwent total hip and total knee arthroplasty were prospectively entered into a clinical anticoagulation trial using a 10-day course of Lovenox with the American College of Chest Physicians-1A guidelines. Major complications occurred in 9% of patients; symptomatic deep vein thrombosis occurred in 9 (3.8%) patients, and nonfatal pulmonary embolism in 3 (1.3%) patients. Complications included 4.7% readmissions, 3.4% return to the operating room for wound incision and drainage, 5.1% prolonged hospitalization (wound drainage), and 3.4% injection site complications. Wound drainage of more than 7 days was predictive of readmission and wound reoperation. A body mass index of more than 35 was predictive of prolonged wound drainage. Return to the operating room for wound complications occurred 3x more frequently with the use of Lovenox than in our previous study using warfarin. Surgical site complications requiring readmission or reoperation should be considered "major" complications.