Recent evidence from well-controlled efficacy studies suggests that diffusing treatment focus across multiple concerns is associated with poorer clinical outcomes. However, research regarding treatment focus diffusion (TFD) in public mental health care (PMHC) settings, broadly or in implemented evidence-based treatments (EBT), is scarce, despite therapists in such settings often reporting more complex cases. Using multilevel modeling, this study examined TFD differences between two in-home PMHC services: (a) Multisystemic Therapy (MST; n=911 youths, 109 therapists), an implemented EBT, and (b) a less structured service more characteristic of treatment as usual (n=2362 youth, 457 therapists). The relationship between TFD and monthly therapeutic progress within and across these two service formats was also examined. Treatment focus diffusion occurred less in the implemented EBT. Overall, receiving services through the less structured service format and more diffused treatment focus predicted less and slower progress over the course of treatment. The relationship between TFD and less clinical progress was stronger in the MST format. These findings held when accounting for indicators of case complexity including initial level of impairment and number of diagnoses. EBTs appear to maintain a narrower treatment focus even when implemented in a public mental health system. However, even in EBTs, TFD predicts poorer clinical progress. Maintaining a narrow treatment focus, even in complex cases typical of PMHC, might improve clinical outcomes.