Juliet Mitchell has made an invaluable contribution to psychoanalytic developmental theory with her elucidation of sibling trauma. She suggests that this is a universal experience of the preoedipal child who becomes aware of the world of similar others through the birth of a sibling or the dawning recognition of the ubiquitous peer group. Suddenly no longer unique, the child is in dread of displacement and confronted with the loss of the special status of “the baby.” Two examples from adolescent analyses are offered to illustrate the power of the lateral dimension.