Hypopituitarism is caused by various insults to the pituitary, such as hypothalamic and pituitary tumors, inflammation, autoimmunity, vascular injury, genetic abnormalities, irradiation, and trauma. Recently, it has been found that autoimmunity to the pituitary involves many pathological conditions associated with specific or non-specific hormone deficiencies in the gland. This review discusses the recent findings on the underlying mechanism of autoimmune hypopituitarism particularly of lymphocytic hypophysitis, IgG4-related hypophysitis, immune checkpoint inhibitor-induced hypophysitis, anti-PIT-1 hypophysitis, and isolated ACTH deficiency.