Introduction Moyamoya disease is a rare and progressive condition with poor long-term prognosis. A meticulous evaluation during an extracranial carotid duplex exam, with attention to subtle changes in anatomy and Doppler signals, can alert the sonographer to pathology in the intracranial circulation, which may suggest this diagnosis. Case Report A 45-year-old woman presented to our vascular lab with an episode of slurred speech, right arm weakness, right-sided numbness, and generalized weakness that lasted 15 – 20 min, with total resolution of symptoms. A carotid duplex examination was ordered and demonstrated no evidence of extracranial carotid disease; however, bilaterally the external carotid artery was larger in size than the internal carotid artery, multiple prominent external carotid artery branches were noted, the internal carotid artery and vertebral artery Doppler signals demonstrated low-resistance waveforms with high diastolic flow velocity, and the left vertebral artery was enlarged. Magnetic resonance imaging with angiography demonstrated multiple intracranial abnormalities, and conventional angiography was compatible with Moyamoya disease. A superficial temporal artery-to-middle cerebral artery bypass was performed with an uneventful postoperative course and no recurrence of symptoms. Conclusions Subtle changes in anatomy and Doppler signals observed during an extracranial carotid duplex examination can be important indicators of pathology in a location that is not under direct visualization and interrogation. It is important for the sonographer to note these changes and report them to the physician for further evaluation by more direct methods of testing. This case provides an example of the use of such indirect sonographic evidence.