Pituitary apoplexy is an ill-defined clinical entity. Some authors include hypoxic pituitary infarction, even in the absence of tumor after hemorrhagic delivery, whereas others apply this term strictly to hemorrhage within a pituitary adenoma. We conducted the present study to establish the prevalence, clinical characteristics, and outcome of pituitary apoplexy, defined as an endocrine crisis characterized by acute intense headache, with or without altered consciousness, rapid development of visual or motor ocular disorders, and pituitary failure, associated with a large pituitary adenoma. We describe 8 consecutive patients (1 woman and 7 men, aged 29-66 yr) presenting over 12 months with pituitary apoplexy. We reviewed patient charts for symptoms, imaging characteristics, hormonal data, management, pathologic findings, and outcome. We examined our pituitary tumors database for cases of macroadenoma without apoplexy occurring during the same period. In 5 patients, potential precipitating factors were present. In 6 patients (3 nonsecreting tumors, 1 free-alpha-subunit-secreting tumor, 1 growth hormone and prolactin-secreting tumor with acromegaly, and 1 prolactinoma), no pituitary disease was suspected before the acute event, representing 19% of newly diagnosed pituitary macroadenomas during the same period of time, a higher proportion than expected from our previously published series. The 2 other patients had known pituitary macroadenomas, a nonsecreting tumor and a prolactinoma on dopamine agonist therapy. Pituitary insufficiency at diagnosis included adrenal failure in 4 patients. Transsphenoidal tumor removal was performed 3-9 days after the onset of symptoms (mean, 5.3 d) in 7 of the 8 patients. Pathologic analysis disclosed tumor hemorrhage in 4 cases, ischemic necrosis in 2, and ischemia after intrasellar hemorrhage in 1. Preoperative magnetic resonance imaging was more sensitive than computed tomography for identifying hemorrhage. The newly diagnosed prolactinoma was treated with dopamine agonist. Complete neuro-ophthalmic recovery was observed in all cases, but only 2 patients displayed normal pituitary function on follow-up. The other 6 patients required long-term hormone replacement therapy. These data show that early surgical decompression prevents persistent neuro-ophthalmic deficit, but does not prevent persistent pituitary insufficiency. Moreover, published data indicate that the efficacy of surgery for the relief of neuro-ophthalmic symptoms decreases with increasing syndrome duration. Our data confirm that apoplexy occurs most often as the inaugural manifestation of pituitary macroadenoma, and suggest a recent increase of cases of apoplexy in our area.