Homocystinuria is the second most common treatable aminoacidopathy. Clinically, affected patients present with eye, skeleton, central nervous system, and most importantly, vascular system abnormalities. This autosomal recessive disorder leads to accumulation of homocysteine and its metabolites in the blood and urine. In this report, we present a case with clinical and biochemical findings of homocystinuria with stroke and a positive familial history of the disease in her brother. A 4-year-old girl was admitted to pediatric emergency ward because of acute onset of right hemiparesis and subsequent generalized tonic-clonic seizures. Cranial magnetic resonance imaging revealed acute infarct areas in the left cerebral hemisphere. Metabolic screening revealed elevated concentrations of serum homocysteine and methionine and a normal serum concentration of vitamin B12. These findings, along with a positive familial history led to the diagnosis of homocystinuria. In any child who presents with stroke, some rare condition such as homocystinuria should be considered in diagnosis.