This Fascicle follows in the wake of the third series Fascicle published in 1997 and two separate sets of second series Fascicles, Tumors of the Extra-adrenal Paraganglion System and Tumors of the Adrenal. In order to attain a better understanding of the varied morphology of neoplasms of the adrenal cortex, medulla and extraadrenal paraganglia, structural aspects of normal anatomy, including hyperplasia, are illustrated. Numerous new illustrations appear in this Fascicle, and a large number have been replaced or upgraded using high quality transparencies for digital imaging. The contributions of cytology and fine needle aspiration biopsy in diagnosis are emphasized, particularly with respect to adrenal tumors. Emphasis is also placed on the important role of molecular pathology and immunohistochemistry in tumor diagnosis, and in some cases may provide valuable information regarding prognosis.