To test the hypothesis that syndrome X is a systemic vascular disorder, the authors studied 40 patients with this diagnosis using technetium-99m hexamethylpropylene amine oxime and single photon emission computed tomography (SPECT) brain images. Twenty-three of 25 cases with definite myocardial perfusion defects diagnosed by thallium-201 myocardial perfusion SPECT also had multiple hypoperfusion areas in the brain versus 2 of 15 patients without thallium myocardial defects. The parietal lobes were the most common hypoperfusion areas, and cerebellum was the least common. Syndrome X is a systemic vascular disorder with a high incidence of hypoperfusion lesions of the brain and is usually coincident with myocardial defects.