Endurance athletes alternate periods of intensive physical training with periods of rest and recovery to improve performance. An imbalance caused by overly intensive training and inadequate recovery leads to a breakdown in tissue reparative mechanisms and eventually to overuse injuries. Tendon overuse injury is degenerative rather than inflammatory. Tendinopathy is often slow to resolve and responds inconsistently to anti-inflammatory agents. Common overuse injuries in runners and other endurance athletes include patellofemoral pain syndrome, iliotibial band friction syndrome, medial tibial stress syndrome, Achilles tendinopathy, plantar fasciitis, and lower extremity stress fractures. These injuries are treated with relative rest, usually accompanied by a rehabilitative exercise program. Cyclists may benefit from evaluation on their bicycles and subsequent adjustment of seat height, cycling position, or pedal system. Endurance athletes also are susceptible to exercise-associated medical conditions, including exercise-induced asthma, exercise-associated collapse, and overtraining syndrome. These conditions are treatable or preventable with appropriate medical intervention. Dilutional hyponatremia is increasingly encountered in athletes participating in marathons and triathlons. This condition is related to overhydration with hypotonic fluids and may be preventable with guidance on appropriate fluid intake during competition.