After many years of advising parents and staff about autism, the author found that one of their most frequent questions was 'Why do they do that?' followed by 'And how can we stop it?'. We do know that children with autism have certain features which clearly distinguish them from other children and that any behaviour management strategies have to be modified to accommodate their unique disabilities. These differences are described in some detail in the hundreds of published research studies and this booklet attempts to apply the results of these studies to explain behaviour patterns and suggest ways of modifying behaviour. Revised edition 2002 available.