Children with intellectual and developmental disabilities suffer more often from pain than their typically developing peers. Their pain can be difficult to manage, and assessment is often complicated by their limited communication skills, multiple complex pain problems and the presence of maladaptive behaviours. However, current research does provide some guidance for assessing their pain. Although self-report is an alternative for a small number of higher-functioning children, observational measures have the most consistent evidence to support their use at this time. For this reason, the Non-communicating Children’s Pain Checklist – Postoperative Version is recommended for children and youth 18 years of age or younger. However, other measures should be consulted for specific applications. Changes in function and maladaptive behaviour should also be considered as possible reflections of pain. In addition, children’s coping skills should be considered because improving these may reduce the negative impact of pain.