A 44-year-old male suffered epistaxis and headache of sudden onset and was diagnosed as having suppurative meningitis due to streptococci. Four days after the onset of symptoms, he died despite treatment with antibiotics. Destruction and ballooning of the sella turcica was revealed by a plain head X-ray examination during the clinical course. At autopsy, a massive tumorous lesion extended from the ballooned sella turcica to the paranasal cavities, nasopharynx and facial bone, and this had resulted in suppurative meningitis. The tumor was also disseminated to the basal skull. The tumor cells possessed prominent nuclear atypia and were immunohistochemically positive for prolactin. This was diagnosed as a case of pituitary adenoma with markedly invasive pathological findings and a rapid and fatal clinical course.