Ornithine transcarbamylase (OTC) deficiency (OTCD) is an X-linked urea cycle disorder. Being an X-linked disease, the onset and severity of the disease may vary among female carriers. Some of them start to develop the disease early in life, whereas others remain asymptomatic throughout their lives. Our patient was a 42-year-old man who developed severe hyperammonemia and fatal brain edema after receiving a right lobe graft from an asymptomatic female living donor with unrecognized OTCD. The donor developed hyperammonemia and disturbed level of consciousness that was managed successfully by hemodialysis. Molecular testing of the OTC gene in the donor revealed a heterozygous nonsense mutation (c.429T > A) in exon 5.