Although children with Williams syndrome (WS) are reported to show a strong motivation towards social interaction, evidence suggests many experience difficulties with peer relations. Less is known regarding the characteristics of such difficulties. Parents and teachers of 21 children with WS (7- to 16 years) completed questionnaires measuring aspects of social functioning and peer interactions. Parents and teachers reported that children with WS demonstrated significantly greater peer problems than population norms, including difficulties sustaining friendships and increased social exclusion. More substantial social functioning difficulties were associated with greater peer relation problems. The study provides multi-informant evidence of peer relationship difficulties in children with WS that require further consideration within the broader WS social phenotype.