This article presented some principles useful in identifying children with neuropsychiatric symptoms who will prove to have metabolic disease. In general, any organic condition that produces cortical dysfunction could present with psychiatric symptomatology. The full range and incidence of neuropsychiatric manifestations are poorly studied for most of these diseases. In most instances, rarity of these conditions precludes any one clinic from collecting a large enough patient base to assess the full range of manifestations. A good deal of the information is based on small series and case reports. At present, because it is not possible to associate a specific cognitive and behavioral profile with a specific metabolic disease, a staged metabolic assessment is indicated in children displaying any of the specific historical features or clinical signs previously noted. It is important to note that the genetic basis, and consequently the fundamental biochemical defect, for most of these disorders has been known for less than a decade. Definitive (gene or enzyme replacement therapy) is therefore at a very early stage for these conditions. It is anticipated that continuing advances in genetics and gene therapy will soon lead to more specific and effective diagnostic and treatment strategies for many, if not all, of these conditions. The child psychiatrist, who may first encounter these patients at an early (and thus more readily treatable) point in the course of illness, will serve an increasingly important role in establishing a correct diagnosis and directing patients to specific therapies as quickly as possible.