Transcranial Doppler sonography (TCD) has been increasingly used to detect embolic signals. A 49-year-old woman had repeated episodes of weakness and numbness of the right limbs. She was diagnosed as having transient ischemic attacks (TIAs). A cranial Gadolinium-enhanced MRI revealed multiple small lesions in the cortical-subcortical areas of the left middle cerebral artery territory. A TCD examination on admission detected 4 embolic signals on the left MCA trunk in a 30-minute examination period. TIAs completely ceased after the initiation of an antiplatelet therapy with aspirin. Embolic signals were not detected in later TCD studies. The embolic signals on the TCD strongly indicated that TIAs are caused by an embolic mechanism. TCD is potentially useful for assessing the efficacy of antiplatelet and anticoagulant therapies in patients with TIAs.