Each field of medicine has a defined scope; however, interactions between systems covered by different fields exist. A link between findings from psychiatry, neurology, immunology and endocrinology has been noted for many years. From the functional, anatomical and physiological perspectives, the correlation between the central nervous system (CNS) and the endocrine system is complex and involves several actors, such as cytokines, receptors and neurotransmitters. The immune system is connected to the endocrine and neural systems via a number of pathways that integrate the functions of the hypothalamus, pituitary glands, adrenal glands, thyroid glands, gonads and autonomic nervous system. Major clinical implications and a vast amount of pathologies are related to the relationships between the systems covered by the science of psychoneuroimmunoendocrinology.