Sustaining evidence-based practices after initial training and support has ended is necessary to ensure lasting improvements in youth mental health services. This study examined factors impacting community clinicians' decisions to sustain a transdiagnostic youth intervention following participation in a study. The aim of the study was to identify potentially mutable factors impacting sustainability to inform future implementation efforts. Thirteen clinicians (85% women, 92% Caucasian, M age = 35.6) completed interviews after participating in an open trial of an evidence-based intervention for depression, anxiety, and conduct disorders. Interviews were analyzed using thematic analysis methods. All (100%) clinicians reported current use of the intervention. Four themes emerged related to sustainability. Clinicians (100%) reported that making modifications, alignment with prior training, and relative advantage influenced their current intervention use. Clinicians (100%) reported that knowledge transfer from treatment developers was vital to sustainability. They (92%) noted a number of logistical, inner-organizational, and client-level barriers to sustainability. Lastly, clinicians (92%) identified factors related to scaling up the intervention. A variety of personal, organizational, logistical, and client variables influence the sustainment of new interventions, and could be leveraged in future implementation efforts.