There is a paucity of knowledge on the role of sibling relationships in internalizing disorders. Research in nonclinical populations suggests an association between internalizing problems in children and negative sibling interactions. Further, an association is reported between internalizing problems and actual or perceived parental differential treatment. This study examines sibling relationship qualities and perceived parental differential treatment in a clinical sample. Participants included 24 anxiety disordered children (ages 8-13 years) and 25 nondisordered control children (ages 7-13 years). Anxiety disordered and nondisordered children do not differ with regard to perceived affection or hostility from a sibling. Anxiety disordered children, however, report significantly more parental differential treatment than do nondisordered children.