This study examined the influence that residential dislocations have on child behavior problems, depression, peer competence, cognitive competence, and the quality of sibling relations in a sample of 70 Head Start children, aged 32 to 67 months, and their older brothers and sisters, aged 48 to 155 months. This was the first study to investigate the sibling relationship in the context of high residential mobility. Information on child characteristics was obtained from mothers and teachers. Sibling data (warmth/harmony and conflict) were obtained from coding videotaped interactions. Child emotionality was found to be an important moderator of the effects of residential mobility on young, poor children and their siblings; caregiver conflict was a less powerful moderator of these effects. Residential instability seemed to compromise the warmth/harmony of the sibling relationship. It was concluded that the effects of residential instability are complex and cannot be understood without considering child characteristics, such as temperament, and the family context in which the child lives.