A case of mother-adolescent son incest is reviewed. The son was treated in psychoanalytic psychotherapy for nine years and seen in a follow-up study five years later. The incest is understood as a compromise formation in which most aspects of the positive oedipus are repressed, while limited direct or defensively altered expression of oedipal and preoedipal impulses are allowed. Superego development is considered as being complete, although the superego is pathologically malformed and is responsible for the patient's pervasive feelings of guilt and his extensive need for punishment for his incestuous behavior. These findings contradict the views of those who understand mother-son incest as representing only direct expression of positive oedipal wishes made possible by a weak, deficient superego.