Comprehension is poor in patients admitted in the emergency observation unit. Teamwork communication gaps could contribute to patients' misunderstanding of their health condition. To determine in patients admitted in the emergency observation unit whether comprehension of diagnosis, prognosis, and management depended on nurses' comprehension, the authors conducted a prospective observational study in a busy adult emergency department of a tertiary teaching hospital in Paris over 2 months. Consecutive patients admitted in the emergency observation unit were included. Patients' and nurses' comprehension of diagnosis, prognosis, and management was compared with the statements of the emergency department attending physicians for these items. The authors observed whether patients' misunderstanding was associated with nurses' misunderstanding. A total of 544 patients were evaluated. For each patient, nurses' and patients' comprehension was available. Patients understood severity in 40%, organ involved in 69%, medical wording in 57%, reason for admission in 48%, and discharge instruction in 67%. In comparison with patients, nurses better understood each item except for discharge instruction. The authors observed that patients' comprehension was better when nurses understood diagnosis (p <.0001), reasons for admission (p =.032) and discharge instructions (p =.002). Nurses' understanding of severity did not modify patients' comprehension. These results support the conclusions that communication gaps in teamwork alter patients' comprehension and that nurses' and patients' misunderstandings are associated. Therefore, improving communication by nurses and physicians to patients may improve patients' understanding.