To investigate the contribution made by autistic children's Challenging Behaviour (CB) to their parents' anxiety and depression, parents of 32 autistic boys and 32 autistic girls (aged 6 to 18 years) completed standardised instruments on their children's behaviour and their own anxiety and depression. Significant associations were found between the children's CB and their parents' anxiety and depression, but the patterns of those associations differed according to the sex of the child. At the individual CB level, boys' change of mood, but girls' social isolation, were most powerfully associated with their parents' depression. Girls' impulsive behaviour was most strongly linked with their parents' anxiety.