Aim: To explore the frequency with which children and young people participate in social activities with peers, when they are affected by Mucopolysaccharidosis I Hurler Disease (MPS IH) post bone marrow transplant (BMT). This was investigated in relation to patient age, and in comparison with a normative sample. Patient withdrawal, adaptive and social skills are also described in terms of patient age and in comparison with a normative sample. Method: Forty-four individuals affected by MPS IH post BMT participated in this investigation. Their ages ranged from 16 months to 25 years. Semi-structured interviews with patients' mothers were utilized, which included the Behaviour Assessment System for Children and a socialization questionnaire. Normative data for the socialization questionnaire were collected from 46 mothers of children not affected by chronic illness or disability. Results: A one-way anova revealed that children not affected by disability or chronic illness (mean=20.63) participated overall in social activities more frequently than children aged under 12 years (mean=14.87) and over 12 years (mean=13.25) who were affected by MPS IH post BMT (F = 21.01, P < 0.001). Young people aged 12 years and over affected by this condition were found to participate in social activities the least. A pattern also emerged, which indicated greater withdrawal and less well-developed adaptive and social skills for MPS IH patients aged 2.5-5 years and 12 years and over, but scores were within the normal range for those aged 6-11 years. Conclusion: These data illustrate a lack of social competency and a tendency towards inhibition and withdrawal in this patient group, particularly among the very young children and the adolescents and young adults. Further research is needed to explore these issues longitudinally and to examine the role played by the family, and indeed disability, in the quality and quantity of social interaction experienced by these individuals.