Abstract Sited at the base of the brain, the pituitary gland, comprising two lobes (anterior and posterior), is linked by a stalk to the hypothalamus and median eminence, which regulate its function. Different cell types in the anterior pituitary secrete growth hormone, prolactin, adrenocorticotrophic hormone, thyroid-stimulating hormone, luteinizing hormone and follicle-stimulating hormone. Cells in the posterior pituitary secrete vasopressin and oxytocin. Adenomas, arising in the anterior lobe, are monoclonal in origin but seldom malignant and may be functioning (hormone-secreting) or non-functioning. They vary in size and extent. They must be differentiated clinically, biochemically and radiologically from other pathologies leading to a sellar or suprasellar mass. Because of their anatomical site and the proximity of other structures, large tumours, in addition to damaging surrounding normal pituitary tissue and leading to hypopituitarism, may expand superiorly to involve the optic chiasm, laterally to involve cranial nerves in the cavernous sinus and inferiorly into the sphenoid sinus. Pituitary adenomas are relatively uncommon and slow-growing tumours, and non-functioning tumours often present late because of the consequences of their size.