BACKGROUND: Cryptogenic stroke leading to cerebellar infarction is a rare but serious cause of acute nausea and vomiting. This has the potential of devastating consequences if this occurs in aviators during flight. We present a case of cryptogenic stroke causing incapacitating nausea and vomiting in a U.S. Air Force pilot.CASE REPORT: A 36-yr-old active-duty U.S. Air Force male pilot developed acute onset severe vertigo, nausea, and vomiting during initial descent. Initial computed tomography imaging was normal and his initial assessment yielded a diagnosis of benign paroxysmal positional vertigo. MRI-Brain at 1 mo revealed a small right inferomedial cerebellar infarct. Echocardiography revealed a patent foramen ovale and bilateral atrial enlargement. He made a full neurological recovery and was eventually returned to active flight status with Flying Class IIC waiver.DISCUSSION: Cryptogenic stroke caused by patent foramen ovale (PFO) is uncommon. However, this is increased in patients younger than 50 yr of age. This can lead to an acute incapacitation with varying degrees of dysfunction. There is controversial discussion of treatment options for secondary stroke prevention with PFO. However, there is no significant literature on primary prevention in these patients. A small subset of patients benefit from closure of PFO and most patients benefit from antiplatelet therapy after a stroke occurs. There may also be a significant subset of patients with PFO that may benefit from antiplatelet therapy as a primary prevention of stroke.Lytle ME, Martin BR. Acute cerebellar stroke in a military active-duty pilot. Aerosp Med Hum Perform. 2021; 92(11): 919-923.