Patients are increasingly being encouraged to take an active role in ensuring their own safety, but doing so will require close partnership between patients and their physicians. However, this survey of hospitalized patients and their physicians revealed fundamental gaps in patients' knowledge of their illness, with nearly 40% of patients being unaware of their diagnosis and 90% being unaware of potential medication side effects. Physicians tended to overestimate patients' understanding of their diagnosis and the plan of care. This study's findings are supported by prior research in the emergency department and outpatient setting. A case of suboptimal communication contributing to patient harm is discussed in this AHRQ WebM&M commentary.