The core problems of autism—those involving social interaction, communication, and restricted and repetitive activities—can be compounded by behavioural problems, including severe tempers, aggression, and irritability.1 Severe aggression places a special burden on carers; it is more common in people with marked intellectual retardation and is related to poor daily living skills and impaired communication. Currently, no drugs are available to treat the underlying autistic condition. Specialised educational programmes, behaviour therapy, and environmental changes can improve aggressive behaviour,1 but if they fail drug treatments should be considered.2 Behavioural problems related to depression or attention deficit can be addressed by relevant therapy; but if the problem of aggression is unresponsive to these manoeuvres the need for symptom control arises. Major tranquillisers in particular have been used off-label, but their place has been uncertain because of doubts about safety and (until recently) efficacy.

Two well conducted double blind placebo controlled studies have compared placebo and the atypical antipsychotic risperidone in children with autism and behavioural problems. One study3 included 101 children with diagnosed autism. The other4 included 79 children with the broader category of “pervasive childhood developmental disorder,” the …