It has been recognized that siblings, their relationships as well as the fantasies, envy and rivalry aroused by them, have been neglected in psychoanalysis. The question has now been raised as to whether completed analysis should always deal with the fantasies aroused by the relationship to siblings as well as parents and the Oedipal situation. This article discusses the resolving of sibling relationships in psychoanalysis. In psychoanalysis, a triangular space is created by the patient, the analyst in transference and the psychoanalytic setting, in this case particularly the function of other patients, representing the patient's siblings or fantasies of siblings. The feelings and fantasies aroused by the other patients originating from sibling relationships in childhood can now be dealt with in analysis. The analyst, in helping the patient to deal with his formerly repressed or denied fantasies, envy and rivalry will become a developmental object that the patient can identify with to create a new psychic structure for thinking about ideas and feelings