Background: Parents often play a lifelong role in supporting their sons and daughters with intellectual and/or developmental disabilities (IDD). There is a need to better understand parent resources, particularly when the individual with IDD has behaviour problems, as the latter has consistently been linked to parental burden. Methods: The current study aimed to investigate the relationship between the behaviour support needs of 212 adults with IDD and parental burden, and whether perceived helpfulness of informal supports moderated this relationship. The helpfulness of individual sources of informal support was also explored. Results: Informal support was negatively related to burden, although it did not act as a moderator. Individual sources varied in terms of how they were related to burden, but none acted as moderators. Conclusions: Although informal social support appears to be important to parents and may help alleviate burden, it does not appear to act as a moderator as anticipated.