General physical education (GPE) teachers often express concerns when asked about including students with autism into an inclusive physical education environment, which typically result in feelings of frustration (Blinde & McCallister, 1998; Goodwin & Watkinson, 2000; Hutzler, Zach, & Gafni, 2005; Place & Hodge, 2001). Similarly, varying levels of self-efficacy and content knowledge related directly to working with students with autism are reported, but research on improving self-efficacy and content knowledge related to this topic is limited. The purpose of this study was to determine the effects of a one day in-service workshop on the self-efficacy and content knowledge of general physical educators to include students with autism into the general physical education setting. The research examined the independent variables of group setting (i.e., treatment versus control). The dependent variables were GPE teacher self-efficacy and content knowledge scores. A mixed-method design was employed for the purposes of this study. Quantitative data was collected using the Physical Educators' Self-efficacy Toward Including Students with Disabilities-Autism (PESEISD-A) instrument given three times (i.e., pretest, posttest, retention) and a content knowledge quiz given two times (i.e., pretest and posttest) (N = 62). The qualitative section involved data collected from a focus group (n = 13) following the in-service. The qualitative data from the focus groups were coded and data were analyzed for emergent themes using content analysis. Results were used to determine the effects of a one day in-service on GPE teacher self-efficacy and content knowledge. The findings from the mixed-methods study indicated that the in-service significantly improved content knowledge scores over time and treatment, but had no statistically significant effect on self-efficacy scores. Overall, GPE teachers expressed positive feelings and perceptions in regards to the in-service and found it to be a valuable professional development opportunity. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]