Autistic youth have an increased risk of mental health problems. Despite the efficacy of various psychotherapeutic approaches for autistic youth, they often do not receive these interventions. Research is needed to identify patterns of effective treatment for autistic youth and whether they differ from those used for youth with other neurodevelopmental conditions (e.g., attention-deficit hyperactivity disorder; ADHD). We compared clinicians' (N = 557) knowledge, confidence and practices when treating autistic youth and youth with ADHD. Although ratings were moderately high overall and similar interventions were used for both groups, clinicians were significantly less knowledgeable and confident when supporting autistic clients compared to clients with ADHD. Thus, improving clinician perspectives may help facilitate treatment for autistic youth with mental health problems.