A 21-year-old woman presented with a 5-day history of loss of appetite, malaise, nausea, and vomiting. On examination, she appeared acutely ill, with jaundice and right-sided hypochondrial tenderness. The stigmata of chronic liver disease were absent, and the results of her neurologic examination were typical. She had previously been well except for bouts of somnolence with occasional emesis during the previous year. There was no history of recent travel, alcohol or illicit drug use, or liver disease in her family. Viral hepatitis was considered the most likely diagnosis, but the patient's clinical deterioration necessitated hospital admission a day later. The results of serology tests for acute infection with hepatitis A virus, hepatitis B virus, or Epstein–Barr virus were negative, and the complete blood count revealed a macrocytic anemia. Liver function tests revealed the following: total bilirubin, 136 μmol/L [upper reference limit (URL),2 26 μmol/L]; direct bilirubin, 62 μmol/L (URL, 7 μmol/L); albumin, 31 g/L [reference interval (RI), 35–50 g/L]; γ-glutamyltransferase, 165 U/L (URL, 44 U/L); aspartate aminotransferase (AST), 166 U/L (URL, 35 U/L); alanine aminotransferase (ALT), 24 U/L (URL, 35 U/L). Serum alkaline phosphatase (ALP) was noteworthy for being undetectable (<5 U/L; RI, 51–117 U/L) on 3 consecutive days.