Delayed onset muscle soreness (DOMS) generally occurs between 24 and 72 hours after a bout of unaccustomed exercise that involves eccentric muscle action. In this review, a variety of aerobic and anaerobic activities are described emphasizing the eccentric component. It is suggested that the experience of severe DOMS can adversely impact various aspects of performance. During endurance events there may be a decrease in economy of movement, impairment of glycogen repletion and an alteration in biomechanical execution of a movement. Reductions in strength/power are also associated with severe DOMS. It is suggested that these changes might put an athlete at increased risk of injury. Although treatment is available to alleviate or prevent DOMS, the wisdom of routinely engaging in such a practice is questioned. Finally, it is noted that one bout of unaccustomed eccentrics results in some adaptation, which has a protective effect during subsequent bouts of eccentric exercise in that DOMS and other markers of muscle trauma are significantly reduced. Recommendations are made for dealing with DOMS at the initiation of an exercise program and during a regular season.