Background: Early detection of cerebral infarction (CI) by home acupuncturists might be helpful in reducing stroke mortality. We compared vital signs of patients who developed CI and those who did not to ascertain if blood pressure balance is a useful marker for the early detection of CI and for distinguishing cases with potentially effective/ineffective acupuncture treatment. Methods: In this retrospective study, vital signs such as body temperature, pulse, and blood pressure, were simultaneously obtained from the right and left arms of patients who received weekly acupuncture treatment. We focused on the differences between values obtained from the right and left arms (the balance) and compared the values of patients who developed CI [CI (+)] (n = 18) and those of age-/gender-matched patients who did not [CI (−)] (n = 18). Results: Left/right blood pressure was significantly more unbalanced in the CI (+) group than in the CI (−) group, especially immediately before the onset of CI. Moreover, all CIs occurred on the side with a lower blood pressure.