Behavioural, cognitive, and affective aspects of social functioning of 107 children with a chronic illness were studied. The aim of the study was twofold: (1) to describe peer interaction of children with a chronic illness in comparison with normative data of healthy children; (2) to examine whether peer interaction was related to the illness characteristics physical restrictions and pain. Peer interaction was assessed with measures of social activities (CBCL), parent-reported social skills (CABS), child-reported social skills (MESSY), social self-esteem (SPPC), and social anxiety (SASK). Results showed no differences between diagnosis groups, suggesting that the social consequences of chronic illness are not diagnosis specific. Compared with healthy norms, chronically ill children reported less aggressive behaviour. The parent-report measures suggested a similar trend. Children with chronic illness also tended to display more submissive behaviour than healthy norms, as perceived by their parents. With regard to illness characteristics, both physical restrictions and pain were associated with restricted social activities, but not with other measures of social peer interaction. Children who display submissive behaviour and children who are restricted in their social activities should receive extra attention because they are especially vulnerable for problems in their social development.