Accurate and timely diagnosis of posterior circulation ischemic stroke is a challenge for emergency neurology clinicians, even MRI scan which is believed to be sensitive to acute ischemic lesions may be negative. It is particularly important to obtain the typical or characteristic symptoms and signs of the patients through comprehensive physical examination. We report a case of posterior inferior cerebellar artery (PICA) territory infarction with "episodic postural diplopia" as the initial symptom, hoping that clinicians notice the vertical diplopia caused by the disfunction of otolith gravity conduction pathway, which is characterized by the degree of diplopia being affected by postural changes. A 44-year-old man was in hospital due to episodic postural diplopia for 4 months, dizziness and unstable walking for 5 days. In the past four months, the patient had endured episodic diplopia attack for 8 times when standing or walking, which could be relieved obviously while lying down and gradually disappeared within 5-10 minutes. He had not seen a doctor since the outbreak of the novel coronavirus. Five days before admission, diplopia worsened accompanying obvious vertigo, nausea and vomiting, left facial numbness, and hiccups. The diplopia could be relieved after taking the supine position, but not completely disappear as before. Physical examination showed a triad of ocular tilt response (OTR), namely static ocular rotation (SOT), skew deviation (SD) and head tilt (HT). And also subjective visual vertical (SVV) deviation was found. Those signs were considered for otolith gravity conduction system involvement. Combined with other clinical signs, such as Horner signs, crossed sensory disorders, ataxia, and MRI scan, it was easy to find the infarction was in the territory of the left PICA. The reasons for the patient's "episodic posi-tional diplopia" in the early stage of the disease were considered as follows: (1) the gravity was less affected in the supine position, the stimulation of the otolith gravity conduction pathway was reduced, so the degree of eye deviation was reduced in the supine position. (2) As an ischemic cerebrovascular disease, the patient experienced a process of transient ischemic attack (TIA) in the posterior circulation, the cerebral blood supply and the hypoperfusion of stenosis were increased after lying down, so the diplopia symptom disappeared. The upright-supine test was recommended for the patients with vertical diplopia. It was recommened to differentiate between otolith pathway involvement and diplopia caused by trochlear nerve palsy.