This study explores the rate of psychosocial dysfunction in affected and unaffected children from families with haemophilia or β-thalassaemia, as part of a cross-sectional, multicentre study into the resilience of 115 families with blood disorders. Sociodemographic and developmental data were collected from the parents using a standardized and semi-structured interview format, and medical data were obtained from the clinician. The children's social functioning over the year prior to the assessment was assessed with The Social Adjustment Scale adapted for school-aged children. Children with β-thalassaemia showed significantly higher rates of social dysfunction than their unaffected siblings or children with haemophilia and their siblings. Older children showed significantly higher social dysfunction at school. The high rate of social dysfunction in children with β-thalassaemia compared with unaffected siblings is likely to have a basis in the negative experiences associated with their medical problems. In contrast, the therapeutic advances in haemophilia allows boys to lead an almost normal life. Overall, the rates of social dysfunction in families with both these disorders proved commoner than reported in population surveys, but with the unavailability of local population controls, caution needs to be exercised in the interpretation of this finding.