Endocrine pathology comprises a spectrum of disorders originating in various sites throughout the body. Some disorders affect endocrine glands, and others arise from endocrine cells that are dispersed in non-endocrine tissues. Endocrine cells can broadly be classified as neuroendocrine, steroidogenic, or thyroid follicular cells; these three families have distinct embryologic origins, morphologic structure, and biochemical hormone synthetic pathways. Lesions affecting the endocrine system include developmental abnormalities, inflammatory processes that can be infectious or autoimmune, hypofunction with atrophy or hyperfunction caused by hyperplasia secondary to pathology in other sites, and neoplasia of many types. Understanding endocrine pathology requires knowledge of both structure and function, including the biochemical signaling pathways that regulate hormone synthesis and secretion. Molecular genetics has clarified sporadic and hereditary disease that is common in this field.