Return to training and competition after deep venous calf thrombosis.Med. Sci. Sports Exerc., Vol. 24, No. 1, pp. 2–5, 1992. A 25-yr-old female triathlete presented with 4 d of increasing left calf pain that started 1 d after an elective termination of pregnancy during the eighth week of gestation. She had been training with running, bicycling, and swimming but did not recall any injury to the calf muscle. Deep venous thrombosis of the calf and popliteal veins was diagnosed, and she was treated with intravenous heparin and oral warfarin anticoagulation. Her major concern was return to training and competition. A protocol was developed based on experience with less active patients and animal studies to allow a progressive return to training activities over 5 wk, followed by running in the sixth week. After release from the hospital, she accelerated the return-to-training protocol and progressed to running within 3 wk. She developed the post-phlebitic syndrome that resolved within 2 yr. The diagnosis and treatment of deep venous thrombosis are reviewed, with specific attention to the needs of athletic patients.