The endocrine system consists of a set of glands that, through the release of hormones and in synergy with the nervous and immune systems, regulate the various organs and apparatuses, contributing to maintaining homeostasis. The communication among the nervous, endocrine, and immune systems includes complex regulatory circuits operating at different functional levels. Laboratory medicine has an essential role in understanding pathophysiological mechanisms involving the endocrine glands and diagnosing diseases affecting the glands. Studying circulating hormone levels provides valuable information to the clinician.