Cytological examination of endocrine tissues in dogs and cats is limited to some neoplastic disorders of the thyroid gland, adrenals, endocrine pancreas and other uncommon neoplasms (chemoreceptor tumours, carcinoids, extramedullary paragangliomas). In fine-needle aspirates (FNA) from normal, hyperplastic and benign neoplastic thyroid tissue, follicular cells are often organised in an acinar arrangement which is reminiscent of the follicular pattern seen on histology. Primary adrenocortical tumours usually cause hyperadrenocorticism in dogs and hyperadrenocorticism or hyperaldosteronism in cats. The normal endocrine pancreas consists of small islands of neuroendocrine cells scattered within the exocrine pancreatic parenchyma. Islet cell tumours are uncommon in dogs and rare in cats. Carcinoids are rare neuroendocrine tumours that arise from neuroendocrine cells dispersed throughout the gastrointestinal tract (gastric and intestinal wall, gall bladder and liver). They have been described mainly in dogs and rarely in cats.