Citrullinemia type 1 is a rare inborn error of urea cycle metabolism caused by variants in the argininosuccinate synthase 1 (ASS1) gene, resulting in deficiency of the ASS1 enzyme.Affected children typically present shortly after birth with hyperammonemic encephalopathy, vomiting, feeding refusal, stroke-like episodes, and seizures, which may be fatal [1].We report an infant with encephalopathy followed by generalized tremor and chorea who was diagnosed with citrullinemia type 1.A 10-month-old girl presented with global developmental delay, excessive crying, decreased limb movements, and 15 days of vomiting after a febrile episode that followed varicella immunization.She had one seizure episode with postictal drowsiness.She was born to nonconsanguineous parents after an uneventful perinatal period.The child was intubated because of drowsiness, and paucity of limb movements on the left side was noted.Blood tests revealed an ammonia level of 285 µmol/L, abnormal liver function test results, and prolonged prothrombin time and activated partial thromboplastin time.There was no evidence of metabolic acidosis.As a urea cycle defect (UCD) was suspected, peritoneal dialysis was initiated, and sodium benzoate was administered to treat hyperammonemia.After regaining consciousness and extubation, she developed generalized tremor, generalized chorea, and perioral dyskinesia while her plasma ammonia level was 1 www.annchildneurol.org