Background: High blood pressure (BP) is a major risk factor for stroke and all of its pathological subtypes including subarachnoid hemorrhage (SAH). However, there is little evidence demonstrating whether failure to have regular BP measured could result in underestimation of people at risk for SAH. Therefore, we aimed to estimate the effects of control of hypertension, diagnosing hypertension, and subsequent regular BP measurement on the risk of SAH in a population-based case-control setting. Methods: In 381 incident SAH cases and 465 frequency-matched community SAH-free controls, data were collected on time of last BP measurement and ever diagnosed and treated hypertension. Results: After adjusting for covariates, the risks of SAH were both significantly higher among individuals who had never had their BP measured (OR: 2.81, 95% CI: 1.27-6.22), who had their BP measured and been diagnosed with hypertension (treated: OR: 1.79, 95% CI: 1.22-2.62; untreated: OR: 1.82, 95% CI: 1.11-3.00), and who had been diagnosed with hypertension but had not had their BP treated or measured in the last year (OR: 4.65, 95% CI: 2.09-10.32). Conclusions: Compared to controls, cases of SAH are more likely to have never had their blood pressure measured and, among those who have been diagnosed with hypertension, cases of SAH are less likely to have had their blood pressure measured in the past year. These results highlight the potential benefits of screening for hypertension and vigilantly controlling hypertension in reducing SAH rate at both population and individual levels.