Although failure to thrive (FTT) is a relatively common presentation in the emergency department, many emergency clinicians are unsure of how to properly work up a pediatric patient with this condition. Obtaining a thorough history and physical examination will likely reveal the cause of FTT. Although most laboratory testing has low diagnostic yield, they may be indicated in certain circumstances. Radiologic testing is normally not indicated unless the history or physical examination point to a specific etiology. This issue reviews the etiology, pathophysiology, and management of patients with FTT, with the goal of improving outcomes while minimizing unnecessary testing, decreasing cost, and expediting emergency department care.