Background: Autism Spectrum Disorder is a neurodevelopmental disorder with unclearly identified psychopathology. Aim:  To assess the severity of autism and psychiatric comorbidity among children with autism. Subjects and Method:Design: A descriptive study was utilized. Setting:  study conducted at outpatient clinics of the Psychiatric Department, Mansoura University Hospitals. Subject:   study include a sample of (84) preschool children diagnosed with autism. Tools: Data collected using three tools; I- Demographic and developmental characteristics of children, and clinical condition of mothers during pregnancy, II- Gilliam Autism Rating Scale, and III- Mini International Neuropsychiatric Interview for children.Results:  Revealed that 72% of studied children with moderate autism severity. Siblings number, age of the mothers during pregnancy, mother comorbid physical complaint during pregnancy, and child age of walking, related significantly to autism severity. More than two thirds (68%) of children with autism comorbid with psychiatric disorders. Anxiety is the most common (35.7%) followed by attention deficit hyperactivity disorder (32.1%). Numbers of comorbid disorders are related significantly to autism severity. Conclusion: Numbers of comorbid disorders related significantly to autism severity. Moreover, the severity of autism related significantly to socio-demographic, developmental characteristics and psychiatric co-morbidity. Recommendations: Caring of comorbid psychiatric disorders may alleviate autistic severity, consequently, comorbid psychiatric disorders should be considered in assessment and intervention of children with autism. Keywords: