Background: Many primary care practices participating in patient-centered medical home (PCMH) transformation initiatives are expanding the work roles of their medical assistants (MAs). Little is known about attitudes of MAs or barriers and facilitators to these role changes.Methods: Secondary data analysis of qualitative cross-case comparison study of 15 New Jersey primary care practices participating in a PCMH project during 2012 to 2013. Observation field notes and in-depth and key informant interviews (with physicians, office managers, staff and care coordinators) were iteratively analyzed using grounded theory.Results: MA roles and responsibilities changed from a mostly reactive role, completing tasks dependent on physician orders during the patient visit and facilitating patient flow through the office, to a more proactive one, conducting previsit planning, engaging in the overall care for patients, and assisting with population management. MAs differed in their attitudes about increased responsibilities, with some welcoming the opportunity to take on expanded roles, others resenting their increased responsibilities, and some expressing insufficient understanding regarding why new tasks and procedures were being implemented.