Background <p>Interventions aimed at juveniles exhibiting challenging antisocial behavior often face motivation issues, high drop-out rates, and difficulties in achieving substantial and long-lasting effects. Gaining insight into how families experience these interventions may be a crucial step in obtaining more understanding of what does and does not work for clients in forensic youth care. The current study investigated the experiences of juveniles and caregivers with Forensic Outpatient Systemic Therapy (FAST), an intensive intervention aiming to reduce juvenile antisocial behavior. The study examined how juveniles and caregivers evaluated FAST in terms of the process of setting treatment goals, helpful components, points of improvement, their therapist, and a blended version of FAST (FASTb) that is partially offered online.</p> Methods <p>Semi-structured interviews were conducted after treatment termination with 24 participants from 16 families (9 juveniles, 15 caregivers) who participated in a randomized controlled trial or quasi-experimental study on the effectiveness of FAST. A purposive sampling method was used to yield a diverse sample and varied experiences. Thematic analysis was performed in three phases.</p> Results <p>Treatment goals were generally set collaboratively and agreement was often achieved, but juveniles were not always involved in setting the treatment goals or in treatment in general. Evaluations of FAST’s success were varied but generally positive. Most helpful treatment components were conversations with the therapist and, to caregivers, program specific components. Although most participants evaluated their therapist positively, some reported the need for more responsivity. FASTb increased treatment accessibility for some caregivers, but most participants preferred face-to-face appointments.</p> Conclusions <p>This study provides insight into how FAST is perceived and factors influencing engagement, yielding several clinical implications for systemic treatment in forensic youth care. First, building a strong therapeutic alliance is important. Juveniles benefit from a kind, activity-based approach, whereas caregivers value therapist empathy. Given the severity of antisocial behavior in FAST’s target group, initial safety interventions may be necessary before being able to invest in the therapeutic alliance. Second, therapists should persist in engaging juveniles, for instance, by incorporating (physical) activities. Third, blended care may improve accessibility. Therefore, it is important to discuss its potential with families throughout treatment.</p>