The early manifestations of hereditary fructose intolerance are described in a series of 55 patients. Management of this metabolic disorder depends on the severity of liver impairment. When the patients are given a fructose-free diet, the improvement is a dramatic but liver enlargement and fatty vacuolization of liver cells often persist. These hepatic findings were also observed in the five homozygous infants who were given a fructose-free diet from birth; this outcome may support the hypothesis that minimal amounts of fructose are esential for human beings.