Hypoplasia of the internal carotid artery is an infrequent congenital anomaly, rarely reported by medical literature. We report a case of stroke in the left medium cerebral artery territory, in which an agenesia-hypoplasia of the right carotid artery was diagnosed. After performing a doppler echography, the following findings led to suspect it: a significant difference between the flow speeds of the internal  carotid arteries through continuous doppler study on the hypoplastic side through the submandibular window; an early disappearance of the spectrum; and the  persistence of an invariable blood flow in the medium cerebral artery on the hypoplastic side when compressing the common carotid artery. With the study of the multi-slice helicoidal computerized tomography, the diagnosis  was confirmed corroborating the existence of hypoplasia of the carotid hole in the skull base. Agenesia was also  found in the distal portion of the internal carotid artery. The left medium cerebral artery was supplied by the basilar  artery through the posterior communicating artery. The relationship with the stroke seems to be casual as shown by the characteristics of neuroimaging.