Lymphocytic hypophysitis is a rarely recognized disease that is characterized by inflammatory infiltration and destruction of the pituitary gland. The etiology of lymphocytic hypophysitis is still unclear, but an autoimmune pathogenesis has been advocated. In fact, histopathologic specimens reveal a diffuse infiltration of the hypophysis by CD3(+) CD4(+) T cells and CD20(+) plasma cells, and antipituitary antibodies are usually found in sera of affected patients. Although previous cases were found to be correlated only to pregnancy and the postpartum period, recent reports in men and women (without association with pregnancy) suggest a possibly higher prevalence of disease. We present the case of a 55-year-old woman affected by an unusually aggressive form of lymphocytic hypophysitis that infiltrated both cavernous sinuses causing bilateral internal carotid artery occlusion and acute ischemic stroke. Diagnosis was achieved with both a biopsy specimen of the pituitary gland and the detection of antipituitary antibodies. The prompt administration of steroid therapy was effective to obtain regression and stabilization of the disease, but both carotid arteries remained permanently occluded. The natural history of lymphocytic hypophysitis is unpredictable. It usually has a benign evolution, but in exceptional cases the inflammatory process may extend beyond the pituitary gland and infiltrate the surrounding structures. These extremely serious consequences highlight the importance of early diagnosis and treatment of this otherwise curable disease.