Using the IOM definition of diagnostic error, this study interviewed hospitalized adults to characterize their experiences with diagnostic errors and their perspectives on causes, impacts and prevention strategies. Nearly 40% of patients interviewed reported at least one diagnostic error in the past 5 years that adversely impacted their emotional and physical well-being. Qualitative analysis revealed five main themes underlying the causes of diagnostic error: problems with clinical evaluation, limited time with clinicians, poor communication between clinicians and patients or between clinicians, and systems failures. Suggested strategies to reduce diagnostic error included improvements to clinical management, increase patient access to clinicians, communication improvements between patients and clinicians and between clinicians, and self-advocacy by patients.