When athletic performance begins to deteriorate, it is important to identify possible underlying etiologies to explain such a phenomenon. Causes include inadequate nutrition, improper training habits, infection, and hematologic or endocrine diseases. In athletes, a thorough investigation of potentially reversible underlying medical conditions may be warranted when there are noted disruptions in training, competition, and recovery. Thyroid disorders should be considered in athletes in whom such a condition is suspected. The clinical picture may not be entirely clear, as athletes may have serum laboratory values that do not accurately correlate with the presenting signs and symptoms, as one might expect. That picture is even further muddled in individuals undergoing significant physiologic stress, and in whom anabolic agents or exogenous thyroid hormone are used. Because there are currently no consensus guidelines on the matter, return to play issues must be addressed when implementing treatment strategies and monitoring serial laboratory values on a case-by-case basis.