INTRODUCTION: Since its introduction in 1982, the TRAM flap has become the mainstay of autologous breast reconstruction. The free TRAM flap, with its low incidence of both total and partial flap loss, is the method of choice in many institutions. Flap failure, while uncommon, is usually secondary to vascular thrombosis. While most series report venous thrombosis occurring within the first 48 hours following surgery, we have observed an unusual occurrence of late venous thrombosis in our free TRAM flap patients. This paper reports on our experience of venous thrombosis in free TRAM flap breast reconstruction, highlighting the significant incidence of late venous thrombosis. METHODS: A retrospective review of all free TRAM flaps for breast reconstruction at our participating institutions was performed identifying patients who had postoperative venous thrombosis. RESULTS: Over 700 free TRAM flaps have been performed at our participating institutions since 1992. Ten patients have developed venous thrombosis. Of these ten, five were discovered in the first 48 hours. The remaining five were not identified until between four and eleven days postoperatively. Four of the patients had already been discharged from the hospital and returned because of changes to their breast reconstruction, while the fifth was discovered on the evening prior to her planned discharge. All five of the flaps with early thrombosis were salvaged by repeat anastomosis. Of the five flaps with late venous thrombosis, two resulted in complete flap loss while the remaining three were salvaged by repeat anastomosis and urokinase infusion. CONCLUSION: The majority of postoperative venous thromboses have previously been reported to occur in the early postoperative period, (within 48 hours). Our experience in free TRAM flap breast reconstruction differs significantly in that half of the thromboses did not occur until the patients were discharged from the hospital or, in one case, on the evening prior to discharge. While we are unclear of the mechanism or prevention of delayed thrombosis, at the minimum patients should be educated on the signs of venous thrombosis and should have a low threshold for contacting their surgeon in the event of any flap changes.