In the spring of 2013, the American Psychiatric Association (APA) published the fifth edition of its Diagnostic and Statistical Manual of Mental Disorders (DSM-5). This brought about many changes in the diagnostic criteria of Autism Spectrum Disorder (ASD), revolutionizing diagnosis of Autism. The purpose of this study is to identify the social workers' perceptions of barriers to implementing DSM-5 in mental health setting in two Arab Countries. A descriptive cross-sectional study using a 31-item questionnaire was conducted with a purposive sample of 51 social workers employed at Autism Spectrum Disorder Care Institutions in both Egypt and Qatar. Findings from this study indicate that there are three types of barriers faced when attempting to use the DSM-5 to diagnose ASD: Practitioners, Organizational, and Client barriers. The results of the study also proved the validity of the study hypotheses. The study also suggested strategies to overcome these barriers.