Background: There are few studies describing remediation for unprofessional behavior in residents and faculty and none that assess the long-term impact of remediation. Objective: We implemented a simulation-based personalized remediation program for unprofessional behavior in residents and faculty and collected assessments from participants and referring supervisors. Methods: Residents and faculty were referred for unprofessional behaviors, including aggressive, condescending, and argumentative communication styles as well as an inability to read social cues. We had standardized patients recreate the scenarios that triggered the unprofessional behavior. After each scenario, participants reviewed a videotape of their performance, participated in guided self-reflection and feedback, and then iteratively practiced skills. In 2017, about 2 to 4 years after the intervention, we conducted structured phenomenological qualitative interviews until thematic saturation was reached. Transcripts were analyzed inductively for themes by 2 reviewers (J.G. and research assistant). Results: Requests for interviews were sent to 16 residents, 8 faculty members, and 24 supervisors, including program directors. Nine remediation participants (38%) and 19 referring supervisors (79%) were interviewed. Sixteen supervisors reported no recurrence of unprofessional behavior in participants 2 to 4 years after the intervention, and participants identified behavioral strategies to reduce unprofessional behavior. Participants and respective supervisors reported similar themes of behavior changes that resulted in improved professional interaction with others. Conclusions: A simulation-based personalized remediation program for unprofessional behavior, where faculty and residents practice behaviors with guided feedback, can lead to sustained positive behavior change in participants.