The effect of twinship on twins themselves has long been studied. In this paper the author investigates the effect of twinship on other members of the family, particularly the siblings. She presents three cases showing that siblings of twins suffer from an intensified sibling rivalry. The mother of twins must in reality devote more time and care to two new babies. In addition, producing twins provides a narcissistic gratification for some mothers whose adulation of their new babies then compounds the hostility and envy normally felt by a single child at the birth of a sibling. Siblings of twins feel excluded from the rest of the family pairs—the father and mother, and the twins. They try to compensate for their feelings of loneliness and incompleteness by unconsciously but unsuccessfully and interminably seeking a twin surrogate.