Multiple deficiencies of vitamins and trace metals have been demonstrated in Down's syndrome. The picture is complex, especially since not all individuals are affected equally. Deficiencies are not age-related, but appear to be lifelong. The brain in Downs's syndrome does not develop adequately; one area, the hippocampus, which is concerned with memory, is poorly developed and is also involved in the pathological changes of Alzheimer's disease. The role of nutrients is discussed in relation to damage to the mature brain, and to the ageing process.