The purpose of this study was to examine the relationship between executive functioning (EF), as manifested in everyday behavior, autism spectrum disorder (ASD) symptoms, and adaptive behaviors in a sample of preschoolers with ASD. Quantitative data from a clinical database were analyzed for this study. Participants in the ASD group (n=52) were a clinically referred sample of children between the ages of 2 and 5.11 years of age. The neuro-typical group (n=50) was an age-, sex- and SES-matched sample selected from the BRIEF-P standardization sample (Gioia et al., 2003). This study examined whether everyday EF impairments existed in a group of preschoolers with ASD compared to a neuro-typical sample using the Behavior Rating Inventory of Executive Functions-Preschool Version (BRIEF-P). Next, the relationship between specific EF domains and ASD symptoms, as measured by the Autism Diagnostic Observation Schedule (ADOS), was investigated for further understanding of the EF construct in the ASD group. Lastly, the study determined if everyday EF measures explain functioning, as measured by parent ratings of positive adaptive behaviors on the Vineland Adaptive Behavior Scales (VABS). The study results provided evidence that preschool children with ASD have significant EF problems as manifested in everyday behaviors and settings compared to an age- and sex-matched neuro-typical sample. The findings revealed a significant negative relationship between the BRIEF-P and the ADOS, indicating that children who received better ratings of EF skills by their parents were observed to have worse ASD symptoms. Finally, there was support for the link between parent ratings of EF skills and parent ratings of adaptive skills. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]