The aim of the present study was to evaluate the feasibility and analyze preliminary data of the effectiveness of affect phobia therapy (APT) adapted to a structured group format. APT is a treatment that targets emotional avoidance and deficiency in emotion regulation that often leads to psychological dysfunction. The target group was patients with comorbid substance use disorder (SUD) and ADHD with core features of affect phobia/emotion dysregulation. Patients in three group treatments with the aim of having eight participants in each group (n = 22) were included in an open design, where targeted symptoms psychological distress, craving, affect phobia, self-compassion, emotion dysregulation, and substance use were evaluated, with repeated measurements every week from the start of therapy to follow-up 4 weeks after the end of treatment. The results showed an increase in self-compassion and a decrease in affect phobia, but no change in symptoms of psychological distress or emotional dysregulation. No reliable reduction in alcohol or drug use could be related to treatment. Craving fluctuated throughout the study period and patients' drinking patterns changed toward more social drinking. The main finding of the study was that affect phobia therapy in a structured group format is a feasible treatment for the patient group and that the therapy showed preliminary effectiveness in increasing adaptive affective functioning and self-compassion. Future randomized controlled trials are needed for conclusive evidence on efficacy, also examining whether the therapy can help reduce substance use.