Surprisingly little has been written on the impact of the death of a baby on an older sibling. This paper describes how a narcissistically vulnerable latency boy grappled, in the course of his psychotherapy, with the painful loss of his baby brother. Emotional and cognitive aspects of his early confrontation with the reality of death are considered. The patient's six theories about the cot death are described. Attention is drawn to the value of the sibling relationship and to the narcissistic needs which this relationship fulfilled. The termination phase is discussed in the light of the dynamics of sudden loss. The safe therapeutic context provided the space in which this young, rather muddled latency boy could grieve and mourn this traumatic loss.