In addition to the already recognized metabolic diseases which have been associated with cataract formation, e.g. galactosaemia, galactokinase deficiency, Lowe's syndrome and diabetes, several other disorders can also lead to the development of cataracts. They are sorbitol dehydrogenase deficiency, uridine diphosphate galactose-4-epimerase deficiency, marginal maternal transferase and galactokinase deficiency, galactitol and sorbitol accumulation of unknown origin, heterozygosity for galactosaemia and galactokinase deficiency as well as the carrier state for Lowe's syndrome. In this review these metabolic disorders have been divided into five groups according to the age at the first appearance of lens clouding and the possible means of treatment have been discussed.