It is often difficult to reconstruct the psychological effect that the birth of a sibling has in a child's life. The author therefore describes the case of a boy whose symptoms of continuously holding his penis developed six weeks after the birth of his sister, and its resolution in a short analysis, as 'further direct evidence that such an event may precipitate anxiety of psycho-pathological proportions'. He leaves open the problems of the exhaustive genesis of the anxiety and whether the treatment should have been continued.