An 18-year-old man was referred to the ER for sudden onset of left hemiplegia, vomiting, and disturbance of consciousness. He was a healthy college student who had never taken any medication before for any disease or illness. There was no exposure to toxins or history of alcohol intake. The patient's family history was significant only for hypertension in his grandmother. A complete system review was negative. His vital signs on admission were as follows: blood pressure, 105/63 mmHg; pulse, 84 beats/min; respiration, 18 breaths/min; and temperature, 36.5°C. Neurological investigation revealed somnolence, global aphasia, gaze palsy, and right-sided hemiplegia. The National Institutes of Health Stroke Scale (NIHSS) score was 15. The patient was transferred to our neurovascular center after 5 h of onset, so thrombolysis with alteplase was not administered. He was not a candidate for acute intervention because multimodal computed tomography revealed no arterial occlusion or perfusion defect (), and after this examination, the patient had significant recovery of his consciousness. His power improved to 4/5 in the affected limbs, bringing his NIHSS score to 1. Treatment of aspirin, clopidogrel, and atorvastatin was administrated. Laboratory parameters on admission indicated an acute bacterial infection with a C-reactive protein (CRP) level of 38.21 mg/L and leukocytosis of 12.71 × 109/L. Neuroimaging with brain magnetic resonance imaging (MRI) showed foci of restricted diffusion in the left thalamus and the right brain stem suggestive of an embolic stroke (). Blood work showed an erythrocyte sedimentation rate (ESR) of 38 mm/h and an antistreptolysin O (ASO) concentration of 290.01 IU/ml. The patient tested positive for antiphospholipid (aPL) antibodies, including antibodies against anticardiolipin (aCL) antibodies, lupus anticoagulant (LA), and β2-glycoprotein-1 (β2GP-1). The β2GP-1 (133 relative unit (RU)/ml) level was elevated in high titers. Hence, a diagnosis of APS was considered. At the same time, a transthoracic echocardiogram (TTE) revealed a BAV with moderate regurgitation and vegetation. The vegetation was attached to the anterior commissure, and the longest oscillating mass was 8 mm. Supported by the infection evidence, we believed septic emboli due to IE should be the primary etiology despite APS. However, the patient developed an increasing fever with shivering after 5 days of antibiotic therapy with high-dose penicillin. Further etiological workup on blood cultures demonstrated the growth of oral Streptococcus, and the patient was transferred to thoracic surgery for aortic valve replacement. Seven weeks after successful mechanical aortic valve replacement, the patient was discharged with only mild unsteadiness. He received a total 6-week course of IV penicillin in the hospital and was advised to continue a long-term warfarin treatment. The patient did not receive any immunotherapy and his aCL, LA, and β2GP-1 tests were still positive in other hospitals in half a year. He had no residual neurological deficits or recurrence of stoke when evaluated 1 year later. The patient had returned to the college and felt that he can live and study as before. The timeline of the case is summarized in ().