Publicly funded mental health services play an important role in serving children with autism spectrum disorder (ASD). Previous research indicates a high likelihood of adaptations when therapists deliver evidence based practices to non-ASD populations, though less is known about therapists' use of adaptations for children with ASD receiving mental health services. The current study uses a mixed quantitative and qualitative approach to characterize the types and reasons therapists adapted a clinical intervention [An Individualized Mental Health Intervention for Children with ASD (AIM HI)] for delivery with clinically complex children with ASD served in publicly funded mental health settings and identify therapist characteristics that predict use of adaptations. The most common adaptations were characterized as "augmenting" AIM HI and were done to individualize the intervention to fit with therapeutic style, increase caregiver participation, and address clients' and caregivers' needs and functioning. No therapist characteristics emerged as significant predictors of adaptations. Results suggest that therapists' adaptations were largely consistent with the AIM HI protocol while individualizing the model to address the complex needs of youth with ASD.