Autoimmune hypophysitis is a rare chronic inflammatory condition of the pituitary gland which typically presents with hypopituitarism and a pituitary mass. Cases involving anterior pituitary alone (65%) are six times more common in women, typically presenting during pregnancy or postpartum (57%). Anterior and posterior pituitary involvement (25%) are twice as common in women, and neurohypophysis alone (10%) occurs equally in both sexes. It has a prevalence of around 5 per million, an annual incidence of 1 in 7 to 9 million and in our experience represents the known or suspected cause of 0.5% of cases of hypopituitarism, <1% of pituitary masses and 2% of nonfunctioning macro lesions presenting to an endocrine clinic. However, 'missed' cases of autoimmune hypophysitis may be the aetiology of some other unexplained cases of hypopituitarism. Clinically, headache and visual disturbance are common. Anterior hypopituitarism shows a characteristic but atypical pattern of deficiency of ACTH followed by TSH, gonadotrophins and prolactin deficiency or hyperprolactinaemia. Eighteen percent of cases have evidence of another autoimmune condition. On magnetic resonance imaging (MRI), autoimmune hypophysitis is typically symmetrical and homogeneous with thickened but undisplaced stalk in contrast to typical findings with pituitary tumours. Ultimately, the histological diagnosis of autoimmune hypophysitis can only be confirmed by surgery but a presumptive diagnosis can often be made on the basis of a combination of context and clinical features, and pituitary biopsy is not always clinically necessary for effective clinical management of the patient.