Diagnostic error research has largely focused on individual clinicians' decision making and system design, while overlooking information from patients. We analyzed a unique new data source of patient- and family-reported error narratives to explore factors that contribute to diagnostic errors. From reports of adverse medical events submitted in the period January 2010-February 2016, we identified 184 unique patient narratives of diagnostic error. Problems related to patient-physician interactions emerged as major contributors. Our analysis identified 224 instances of behavioral and interpersonal factors that reflected unprofessional clinician behavior, including ignoring patients' knowledge, disrespecting patients, failing to communicate, and manipulation or deception. Patients' perspectives can lead to a more comprehensive understanding of why diagnostic errors occur and help develop strategies for mitigation. Health systems should develop and implement formal programs to collect patients' experiences with the diagnostic process and use these data to promote an organizational culture that strives to reduce harm from diagnostic error.