Lymphocytic hypophysitis, a rare disease hitherto restricted to women, usually presents with symptoms of hypopituitarism in relationship to pregnancy. Two patients who developed pituitary insufficiency from lymphocytic hypophysitis are described. In the first, visual deterioration due to chiasmal compression from hypophysitis arising in ectopic pituitary tissue responded to bromocriptine and corticosteroids. In the second, an insidious onset of hypopituitarism occurred over 5 years in an elderly male. Combined HLA and complement typing confirmed that both patients shared MHC class I, II and III alleles. These class II and III alleles have been described in association with Hashimoto's thyroiditis and insulin-dependent diabetes mellitus (IDDM), both of which may be associated with antipituitary antibodies. The features of these two cases extend the known clinical and pathological spectrum of this disease and, through identifying a common immunogenetic background, provide a possible link between the previous associations of this disorder and autoimmune thyroid disease and IDDM.