We encountered three cases of unilateral absence of the external carotid artery. We were able to find only Franklin's case reported in the literature published to date. The absence of the external carotid artery has been explained as due to the fact that the development of the external carotid artery arising from the ventral aorta was disturbed by unknown factors in the early embryonic stage. In the process of embryonal development, the internal carotid artery and branchial arteries (that are to be components of the external carotid artery) have remained without connection and without development of the ECA trunk. The final result is that the branches of the external carotid artery originate directly from the carotid artery. The existence of dextrocardia in case 2 and an azygos anterior cerebral artery in case 3 suggests that the absence of the external carotid artery occurred during the early embryonal stage due to unknown factors. Angiography is essential to make a diagnosis of the absence of the external carotid artery. However this time ultrasound sonography was very helpful towards further delineation of ulceration and thickening of the intima-media complex that were not diagnosed by angiography. The ultrasound sonographic findings and operative findings revealed characteristic rudimentary findings of ECA aplasia. In particular, this ulceration has a shape like a broad-based volcano that is hollow inside.