This paper reviews galactosaemia and describes the experience of the Willink Biochemical Genetics Unit in the management of classical galactosaemia. Galactokinase and UDPgalactose-4-epimerase deficiency are dealt with briefly. The former disorder is readily treated with a galactose free diet and if this is started early in life, the only complication, cataracts, is avoided. Epimerase deficiency is a relatively 'new' disorder and little is known about the eventual outcome of affected patients. Early observations suggest that the prognosis is likely to be poor even in those patients diagnosed and treated soon after birth. Classical galactosaemia leads to a number of long term complications. The prognosis for normal mental development in affected patients is poor. Unfortunately this does not appear to be reversible by early diagnosis and treatment and whilst every effort should be made to establish an early diagnosis our experience suggests that there is no difference in the ultimate mental development between those who are detected within the first two weeks of life and those before the age of six weeks. In addition female homozygotes are at a very high risk of developing ovarian failure at an early age.