Chromogranins belong to the family of secretory chromogranin and secretogranin proteins. They are found in secretory vesicles throughout the neuroendocrine system. Chromogranin A (CgA) is the main component. CgA acts as a prohormone submitted to processes of degradation through which active peptides are generated. CgA has auto, para and endocrine functions. It is widely used as an immunohistochemical marker. Despite the lack of international standardization, and the lack of an accurate definition of the diagnostic cut-off levels, some CgA assays are reliable. Numerous studies have suggested that CgA determination may be of interest for the diagnosis and the follow-up of various endocrine tumors. Plasma levels of this general marker are proportional to tumor mass. The localization of the primitive tumor, the presence of associated hormonal secretions and possible renal failure and/or hypergastrinemia must be taken into consideration for proper interpretation of CgA levels. New clinical indications are emerging for the evaluation of stress in intensive care units and the assessment of cardiovascular risk. New assays estimating the concentration of active peptides are under development.