Barth syndrome is a rare, x-linked genetic disorder. Few studies have examined psychosocial functioning in this population. The current study examined the psychosocial adjustment in individuals with Barth syndrome, as well as their parents. A secondary aim was to examine demographic as well as psychological correlates and predictors of poorer adjustment in order to identify relevant areas for intervention. Individuals with Barth syndrome completed measures of psychosocial functioning, health-related quality of life, and attitudes toward their illness. Parents completed measures relating to their child’s psychosocial functioning and reported on their own psychological functioning and coping. Results indicated that the majority of individuals and parents reported normative levels of psychological functioning. Younger age was associated with poorer health-related quality of life in some domains. Increased levels of internalizing symptoms were associated with poorer psychosocial functioning in individuals with Barth syndrome. Having a child with externalizing symptoms was associated with increased emotional symptoms for parents, as were certain maladaptive coping strategies. Clinical implications are discussed.