Gastrointestinal (GI) illnesses are common in athletes. Various causes include adverse physiologic adaptations of the gut during exercise; excess ingestion of carbohydrate drinks, alcohol, and anti-inflammatory medications; emotional stressors; exposure to pathogens in closed environments and during travel; trauma; and abdominal wall pressure overload. Unfortunately, evidence-based management of GI illnesses in athletes is limited because most studies have compared various GI illnesses between different sports, rather than comparing athletes to nonathletes. This article reviews the evidence that is available specifically relating to etiology, pathophysiology, clinical presentation, relevant differential diagnoses, acute management, and recommendations for specialist consultation of various GI illnesses in the training-room setting.