A 1-3/12-year-old Turkish boy born of consanguineous parents was hospitalized in poor general condition with disorientation, hepatosplenomegaly, and rickets. Laboratory tests showed pronounced symptoms of hepatic dysfunction, rickets, and Fanconi's syndrome with acidosis. The diagnosis juvenile type I tyrosinemia was based on the anamnesis, hepatorenal symptoms, and elevated tyrosine and methionine blood levels as well as the pathognomic findings of heavy succinylacetonuria and absent fumarylacetoacetase activity in the fibroblasts. Etiology, pathobiochemistry, clinical symptoms, differential diagnosis, and therapy of this rare autosomal-recessive inherited metabolic disease were discussed.