Records were reviewed by 1 of 3 reviewers—2 emergency physicians (S.P.F. and D.B.B.) and 1 fourth-year emergency medicine resident (J.F.C.)—and data were entered into a standard form. Interrater reliability was not evaluated. Data collected included age, sex, initial blood pressure, number of blood pressure checks on the day of presentation, previous history of hypertension, serious and minor symptoms, tests or medications administered or prescribed in the ED, admission or discharge information, final diagnoses, and return visits. Blood pressure was considered normal if the systolic blood pressure was less than 140 mm Hg and diastolic blood pressure was less than 90 mm Hg. Final diagnoses were reviewed for ED visits, hospital stays, and ED revisits at any hospital in the network within 7 days of presentation. Outcome was defined as the presence or absence of 1 of the following acutely serious final diagnoses: myocardial infarction, angina, coronary syndrome, congestive heart failure, pulmonary edema, hypertensive encephalopathy, malignant hypertension, stroke, transient ischemic attack, subarachnoid hemorrhage, loss of vision, kidney failure, or aortic dissection. Accelerated hypertension or hypertensive urgency was not considered a serious diagnosis by itself. Hospital admission by itself was not considered a serious outcome, because patients might be admitted for blood pressure concerns (hypertensive urgency) only. Final diagnosis was considered the diagnosis in the ED medical record or, if the patient was admitted to the hospital, the diagnosis listed in the discharge summary of the patient's medical record.