Tyrosinemia type 1 is an autosomal recessive inborn error of tyrosine metabolism that caused a mutation in the gene coding for the enzyme fumarylacetoacetate hydrolase(FAH). As a result, maleylacetoacetate(MAA) and fumarylacetoacetate(FAA) are formed. The accumulated FAA is converted into succinylacetone(SA) and succinylacetoacetate(SAA) which are excreted in urine. The first report with typical clinical and biochemical findings was presented by Sakai in 1957. Clinically, the disorder is characterized by progressive liver damage with liver failure, a high risk of hepatocellular carcinoma and renal tubular dysfunction hypophosphataemic rickets. Some patients have porphyria-like episodes. Liver transplantation has been the ultimate treatment of tyrosinemia. However pharmacological therapy with 2-(2-nitro-4-trifluoromethylbenzoyl) -1,3-cyclohexanedione(NTBC) has offered a new therapeutic option in addition to dietary restriction of tyrosine and phenylalanine. We experienced a case of tyrosinemia type 1 with cytomegalovirus infection in a 4-month-old male who improved by dietary restriction of tyrosine and phenylalanine.