Forty years after Kanner's seminal article, experts continue to disagree about the definition, reliability and usefulness of the Early Infantile Autism (EIA) syndrome. The ongoing controversy is fuelled by misconceptions about the purpose of diagnosis, by the use of various diagnostic criteria and a failure to consider whether the EIA diagnosis is useful in a practical sense. In the present article, the EIA syndrome is examined from three perspectives. The first addresses the general question of whether identifying childhood psychotic syndromes is a worthwhile enterprise. Next, evidence for the reliability of the EIA syndrome is reviewed. Finally, the usefulness of considering EIA a discrete syndrome is examined. It is concluded that: (a) identifying syndromes of childhood psychosis is not only worthwhile but crucial for progress in research and treatment; (b) EIA can be reliably diagnosed and, (c) there is evidence supporting the usefulness of the EIA syndrome.