This study tested the feasibility and initial efficacy of a cognitive-behavioral summer treatment (summerMAX[superscript yc]) for high-functioning young children, ages 4-6 years, with ASD (HFASD; without intellectual disability). The treatment was conducted 5 days per week, 6 h per day, over 5 weeks in the summer and included skills instruction and therapeutic activities targeting social/social-communication skills, facial-emotion recognition, and interest expansion. Skills instruction sessions and therapeutic activities utilized direct instruction, modeling, role-play, performance feedback, and repeated practice. A behavioral system was also implemented to increase skills development and reduce ASD symptoms and disruptive behaviors, and parents participated in weekly parent training. Feasibility was supported in high levels of treatment fidelity and child, parent, and staff clinician satisfaction, and there was no attrition or adverse events/responses. Results of the primary outcome measure (coding of the children's social performance by naïve raters) indicated that 10 of the 12 children were treatment responders (d = 1.76). Significant post-treatment improvements were also found on secondary measures (parent and staff clinician ratings) of social/social-communication skills and ASD symptoms, as well as a range of adaptive behaviors (effect sizes in the medium and large ranges). Results supported the feasibility of the treatment and suggested that it may yield positive outcomes for 4-6 year olds with HFASD. Recommendations for ongoing testing are provided.