agenesis of the internal carotid artery (ICa) is an extremely rare congenital anomaly and the association of ICa agenesis and tremor is less common. We present an unusual case of left ICa agenesis, which is associated with tortuous distal basilar artery and a dolichoectatic left posterior communicating artery (pCoM) with compression of left subthalamic nucleus (STN). a 67-year-old, right-handed woman, presented at our clinic with postural and rest tremor of the head and right upper limb. a computed tomography angiogram revealed agenesis of the intracranial portion of left ICa and complete absence of carotid canal of the left temporal bone. a digital subtraction angiography of the left vertebral artery showed a kink of distal basilar artery and a dilated, calcified left pCoM, which supply the left middle cerebral artery. This prominently enlarged collateral vessel compresses the left STN and determines the tremor of head and right hand.