A group of 273 children and adolescents, aged 8 to 19 years, who had been treated for a congenital malformation during their 1st month of life, were studied using psychiatric interviews with the child and at least one of his parents. The child was also given a Wechsler intelligence test. The rate of psychopathological disturbance was as high as 49% (the classification used included organic brain disorder and mental retardation). Developmental deviations, psychoneurotic disorder and reactive disorder were the commonest types of disturbance (in 18, 17, and 11% respectively). Eleven percent were suffering from organic brain disorder and 8% had an IQ of no more than 50. The malformed children were compared with 509 children from the general population in terms of behaviour disturbance as rated by their teacher. Approximately one child in five in both groups presented behaviour problems, and behaviour was labelled as antisocial in 10% of children in both groups. The two groups of children did not differ significantly in regard to the family's social class, annual income, father's educational background, or the number of children in the family, but the parents of the malformed children had recieved psychiatric treatment more often than the control group parents.