Tyrosinemia type I is an inborn error of metabolism caused by a deficiency in the last enzyme of the tyrosine catabolic pathway, fumarylacetoacetate hydrolase (FAH). The disease has been reported worldwide with varying incidence. Recently, there has been considerable progress in identifying mutations in the FAH gene. At present 26 mutations have been reported, all consisting of single base substitutions resulting in 16 amino acid replacements, one silent mutation causing a splicing defect, five nonsense codons, and four putative splicing defects. The location of these mutations is spread over the entire FAH gene, with a particular clustering between amino acid residues 230 and 250. The identification of these mutations in subpopulations and groups at high risk should help in the diagnosis of, and genetic counseling for, HT1. We describe all these 26 mutations reported so far and their implication in diagnosis and carrier detection.