The case of a 56-year-old man with sudden onset of retrobulbar headache and progressive loss of vision in his left eye is described. The anatomical position of the chiasm noted during surgical resection of a necrotic pituitary adenoma accounted for this patient's presentation of monocular blindness. We discuss the typical features of pituitary apoplexy and provide a pathophysiological explanation of these signs and symptoms. A differential diagnosis is given and appropriate treatment is described.