A distinction is made (British Medical Journal, 1978; Munro, 1980) between an excessive preoccupation with minor bodily defect, dysmorphophobia, and monosymptomatic psychosis in which a delusion of bodily change may be the sole symptom of an underlying schizophrenic or depressive illness. Hay (1981) has argued for careful distinction between the over-valued idea of dysmorphophobia and the delusion of depressive or schizophrenic illness. But in the absence of any features suggesting psychosis, scrutiny of the abnormal belief in isolation may fail to detect which sort it is. Riding and Munro (1975) hold the distinction to depend upon assessment of the abnormal belief as being of ‘neurotic’ versus ‘delusional’ intensity and of the degree of personality involvement. Andreasen and Bardach (1977) have proposed formal diagnostic criteria incorporating similar features: the dysmorphophobic symptom of excessive concern with appearance, the desire for surgery or underlying presence of personality disorder, and the absence of psychotic symptomatology. However, judgements of ‘neurotic’ versus ‘delusional’ intensity, of absence of psychotic symptomatology and of personality involvement may be particularly difficult against a background of developing personality and in adolescence the problem may be further compounded by the cumulative and recursive effects upon personality development of psychological disturbance.