Life-threatening illnesses in children have a significant impact on the lives of their brothers and sisters. Consequently, special attention must be paid to the specific needs of these siblings to help them cope with their situations. To address this issue, we developed an inventory of the needs of the adolescent siblings of severely ill children, the Inventaire des Besoins de la Fratrie d'Enfants Malades Severement (IBesFEMS) [Needs Inventory for Siblings of Critically Ill Children]. The present article describes a preliminary validation study of this new instrument.