The conditions of childhood that follow prenatal or perinatal problems are defined. These conditions are mental retardation in varying degree, the cerebral palsies, the syndrome of minimal cerebral dysfunction, language disorders and defects of hearing and vision. The difficulties in accurately measuring disability and handicap are discussed and an estimate of the size of the problem is offered. The contribution made by the low birthweight group is also considered and it is pointed out that, although within this group there is a much higher incidence of problems, the majority of children with handicapping conditions were of normal birthweight.