Background: Poor-grade subarachnoid hemorrhage (SAH) has been associated with a high case fatality, either in the acute phase or in the later stages. The exact causes of death in these patients are unknown. Methods: We performed a retrospective study of all consecutive patients with SAH with World Federation of Neurosurgical Societies grade IV or V on admission from 2009 to 2013 at 2 tertiary referral centers in Amsterdam, the Netherlands, and Toronto, Ontario, Canada, who had died during their hospital stay. Results: Of 357 patients, 152 (43%) had died. Of these 152 patients, 87 (24%) had not undergone aneurysm treatment. The median interval to death was 3 days (interquartile range, 1–12 days) after initial hemorrhage. The major cause of death in both centers was withdrawal of life support (107 patients [71%]; 74 of 94 [79%] in Amsterdam and 33 of 58 [58%] in Toronto; P < 0.01), followed by brain death in 23 (15%; 16 of 58 [28%] in Amsterdam vs. 7 of 94 [7%] in Toronto; P < 0.01). The remaining causes of death represented <15%. Conclusions: The decision to withdraw life support was the major reason for death of patients with poor-grade SAH for an overwhelming majority of the patients. The exact reasons for withdrawal of life support, other than cultural and referral differences, were undetermined. Insight into the reasons of death should be prospectively studied to improve the care and clinical outcomes of patients with poor-grade SAH.