Psychotherapy incorporating horses (PIH) is a specialized form of therapy that uses structured, ground-based interactions with horses. This study examined the effects of PIH in therapy-resistant adolescents with autism spectrum disorder (ASD) and explored gender differences in treatment response. A randomized, multiple-baseline single-case experimental design was used with 10 participants who received a 15-week structured PIH intervention (the Pegasus Protocol). Emotional dysregulation was assessed across two domains, reactivity and dysphoria, using the short form of the Emotion Dysregulation Inventory (EDI). While most participants demonstrated small to large decreases in dysregulation scores during and after the intervention, none of the changes reached statistical significance in randomization tests using the Tau-U non-overlap index. No significant gender differences were found. These findings should be interpreted in light of several methodological limitations, including small sample size and short baseline and post-intervention phase. Future research should include context-sensitive measurement tools and alternative analytic approaches. Despite these limitations, the study offers preliminary insight into the individualized effects of PIH and highlights the need for more rigorous, larger-scale investigations in this emerging field.