Sustainment of evidence-based practices is necessary to ensure their public health impact. The current study examined predictors of sustainment of Parent-Child Interaction Therapy (PCIT) within a large-scale system-driven implementation effort in Los Angeles County. Data were drawn from PCIT training data and county administrative claims between January 2013 and March 2018. Participants included 241 therapists from 61 programs. Two sustainment outcomes were examined at the therapist- and program-levels: 1) PCIT claim volume and 2) PCIT claim discontinuation (discontinuation of claims during study period; survival time of claiming in months). Predictors included therapist- and program-level caseload, training, and workforce characteristics. On average, therapists and programs continued claiming to PCIT for 17.7 and 32.3 months, respectively. Across the sustainment outcomes, there were both shared and unshared significant predictors. For therapists, case-mix fit (higher proportions of young child clients with externalizing disorders) and participation in additional PCIT training activities significantly predicted claims volume. Furthermore, additional training activity participation was associated with lower likelihood of therapist PCIT claim discontinuation in the follow-up period. Programs with therapists eligible to be internal trainers were significantly less likely to discontinue PCIT claiming. Findings suggest that PCIT sustainment may be facilitated by implementation strategies including targeted outreach to ensure eligible families in therapist caseloads, facilitating therapist engagement in advanced trainings, and building internal infrastructure through train-the-trainer programs.