Four glaucoma patients with rapid progression of visual field damage and excavation of the optic nerve head despite normal or well-controlled intraocular pressure had one factor in common: low systemic blood pressure. Furthermore, when monitored during 24 h, a sustained blood pressure drop during sleep was always observed. Systemic hypotension, therefore, might be a significant risk factor for glaucomatous damage. The authors recommend measuring the blood pressure frequently in such patients, especially at night.