Anger related behaviours such as aggression are known to be an area of difficulty for children with autism spectrum disorders (ASD). A national internet forum for parents of children with ASD was selected out of other similar forums from six English speaking countries. Information about the angry episodes of 121 children with ASD as described by 120 parents on this forum was analysed. From the parents' perspective, children with ASD were angry frequently with aggressive behaviours, their anger was target and context specific, and they could not control their own behaviours during their angry episodes but some were apologetic afterward. These behaviours impacted on the whole family, their parents, their siblings and the children with ASD. These episodes were influenced by their being physically or emotionally unwell, and antecedents included inaccessibility to preferred items, and changes in routines/environments. There might be improvement over time and possible gender difference in these behaviours.