Zinc is an abundant trace element in the human body that is essential for growth and development and immune function. It is important for the formation of biomembranes and zinc finger motifs found in DNA transcription factors and has catalytic function in metalloenzymes. The intestine is the site of zinc absorption and the major route of zinc excretion. Dietary inadequacy or conditions that decrease zinc absorption or increase its losses from the gastrointestinal tract, urine, or skin may quickly cause zinc deficiency due to the limited availability of rapidly exchangeable zinc pools in the body. Diarrhea is both a sign and a cause of zinc deficiency. The mechanism by which zinc deficiency causes diarrhea is not known. At this time, there is no readily available sensitive test for the detection of zinc deficiency, and therefore clinical suspicion remains the main mode of detection. In some individuals with diarrheal disease, zinc supplementation lessens diarrhea. Those receiving prolonged supplemental zinc therapy need to be monitored for copper deficiency.