Introduction: There are few primitive arterial connections present between primitive carotid artery and primitive basilar artery which usually regresses and disappears except posterior communicating artery (PCoA) and if they fail to regress they are termed persistent carotid–basilar anastomosis (PCBA) which has 4 types– namely persistent trigeminal artery (PTA), persistent otic artery, persistent hypoglossal artery and proatlantal intersegmental artery. Case report: We reported the case of 54 year old male with chronic hypertension having complaint of acute onset of right sided hemianopia for which MRI imaging revealed thrombotic occlusion of left posterior cerebral artery with changes of subacute infarction in its territory and accidental finding of right sided persistent trigeminal artery (PTA) – type of persistent carotid–basilar anastomosis (PCBA). Discussion: Persistent trigeminal artery (PTA) arises from junction between petrous and cavernous part of ICA and communicates with basilar artery and is most common type of persistent carotid–basilar anastomosis and is usually unilateral. There are two types of PTA noted according to Saltzman classification. Diagnosis of PTA is made on angiographic images which on sagittal sections show classical “Neptune’s trident configuration” also known as “Tau sign”.