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Little is known about activities that trigger rupture of an intracranial aneurysm. Knowledge on what triggers aneurysmal rupture increases insight into the pathophysiology and facilitates development of prevention strategies. We therefore aimed to identify and quantify trigger factors for aneurysmal rupture and to gain insight into the pathophysiology.During a 3-year period, 250 patients with aneurysmal subarachnoid hemorrhage completed a structured questionnaire regarding exposure to 30 potential trigger factors in the period soon before subarachnoid hemorrhage (hazard period) and for usual frequency and intensity of exposure. We assessed relative risks (RR) of rupture after exposure to triggers with the case-crossover design comparing exposure in the hazard period with the usual frequency of exposure. Additionally, we calculated population-attributable risks.Eight triggers increased the risk for subarachnoid hemorrhage: coffee consumption (RR, 1.7; 95% CI, 1.2–2.4), cola consumption (RR, 3.4; 95% CI,1.5–7.9), anger (RR, 6.3; 95% CI, 4.6–25), startling (RR, 23.3; 95% CI, 4.2–128), straining for defecation (RR, 7.3; 95% CI, 2.9–19), sexual intercourse (RR, 11.2; 95% CI, 5.3–24), nose blowing (RR, 2.4; 95% CI, 1.3–4.5), and vigorous physical exercise (RR, 2.4; 95% CI, 1.2–4.2). The highest population-attributable risks were found for coffee consumption (10.6%) and vigorous physical exercise (7.9%).We identified and quantified 8 trigger factors for aneurysmal rupture. All triggers induce a sudden and short increase in blood pressure, which seems a possible common cause for aneurysmal rupture. Some triggers are modifiable, and further studies should assess whether reduction of exposure to these factors or measures preventing sudden increase in blood pressure decrease the risk of rupture in patients known to have an intracranial aneurysm.