Hemorrhagic transformation (HT) of an ischemic stroke within 6 hours has never been documented. We reported a case of 65-year-old female experiencing sudden onset of slurred speech and right side weakness. Her past history disclosed rheumatic heart disease and atrial fibrillation. The National Institutes of Health stroke scale (NIHSS) score was 20. The brain computed tomography one hour after symptom onset revealed a faint hypodense lesion in the left striatum. The lesion, however, was transformed spontaneously into a large hematoma within 3 hours of symptom onset. This case thus developed a very early HT of a subcortical infarct of possible cardioembolic origin and high initial NIHSS score. Though rare, very early spontaneous HT does happen.