Among 50 adults hospitalized for non-cardiac conditions who had asymptomatic blood pressure readings of 140/90 mmHg or higher on at least two occasions 24 hours apart, 84% (95% CI 70.9–92.8) met criteria for hypertension on 24-hour ambulatory monitoring four weeks after discharge. That included 86% of those with no prior diagnosis and 83% of known hypertensives, who remained uncontrolled. Standardized research readings, but not routine ward readings, tracked with follow-up ambulatory values. Because treating physicians changed therapy in 52% of patients, usually by de-escalating, the findings cut against the assumption that hospital elevations are just pain, stress or fluid shifts. This is a preprint, not yet peer reviewed, so conclusions may change. The sample is small and from a single setting, there is no comparison group with normal in-hospital readings, and the 84% figure cannot show how many normotensive inpatients would also be hypertensive later, so the predictive value of an elevated reading remains unquantified. Still, ambulatory monitoring is the reference standard, and the clinical message is practical: an elevated reading during a hospital stay deserves out-of-hospital follow-up rather than dismissal, especially in people never diagnosed. Hypertension is a leading modifiable driver of stroke, heart disease and dementia, and undiagnosed cases are common. The work is incremental and confirmatory in spirit, but it adds prospective data to a question where guidance has been thin. Anyone discharged after a hospital stay with high readings should ask about home or ambulatory monitoring.