Pervasive developmental disorders is umbrella of five disorders: Autistic disorder, Asperger's disorder, Pervasive developmental disorder not otherwise specified, Rett’s disorder and Childhood disintegrative disorder. Each one differ than other in degree of symptoms. Generally, all of them called autism. High functioning autistic children are better in response to treatment by either hyperbaric oxygen therapy or combination of hyperbaric oxygen therapy and Risperidone. They have better cognitive abilities. Therefore, this study aimed to determine effects of hyperbaric oxygen therapy and Risperidone in decreasing degree of autism and to predict risk factors that leads to sever autism. The sample consisted of 80 Egyptian autistic children aged 5-7.They diagnosed and followed up by Childhood Autism Rating Scale, version2 (CARS2) between 2015 and 2017. Our studied sample were (80%) male and (20%) female, after adjustment for familial, socio-demographic and individual factors. We concluded that hyperbaric oxygen therapy alone or combination of hyperbaric oxygen therapy and Risperidone has superior effect than Risperidone alone in decreasing degree of autism. In addition, positive consanguinity is a risk factor for severity of autism.