People with serious mental illness (SMI) have lower rates of use of preventative medical services and higher rates of mortality compared to the general population. Research shows that specialized primary care medical homes improve the health care of patients with SMI and are feasible to implement, safe, and more effective than usual care. However, specialized medical homes remain uncommon and model dissemination limited. As part of a controlled trial assessing an SMI-specialized medical home, we examined clinician and administrator perspectives regarding specialized versus mainstream primary care and identified ways to enhance the scale-up of a specialized primary care model for future dissemination. We conducted semistructured interviews with clinicians and administrators at three sites prior to the implementation of an SMI-specialized primary care medical home (n = 26) and at 1-year follow-up (n = 24); one site implemented the intervention, and two sites served as controls. Interviews captured service design features that affected the quality of care provided; contextual factors that supported or impeded medical home implementation; and knowledge, attitudes, and behaviors regarding the care of patients with SMI. Interviews were transcribed and coded. Clinicians and administrators described SMI-specialized primary care medical homes as advancing care coordination and outcomes for patients with SMI. Stakeholders identified elements of a specialized medical home that they viewed as superior to usual care, including having a holistic picture of patients' needs and greater care coordination. However, to enable scale-up, efforts are needed to increase staffing on care teams, develop robust clinician onboarding or training, and ensure close coordination with mental health care providers. (PsycInfo Database Record (c) 2024 APA, all rights reserved).