Researchers looked at the age, health and treatment of more than 10,000 patients in 25 hospitals across Scotland on a single day.
The findings of the survey, the first of its kind in the world, showed that 28.8% of patients were likely to die within 12 months of a hospital admission.
The researchers, from Glasgow University, suggest more work needs to be done to recognise when patients are nearing the end of their lives and their potential need for palliative care.
Of the 10,743 patients in the study, the majority (64.1%) were aged 65 or over and 54.7% were women, 45.3% men.
The survey found that men are more likely to die than women for the majority of age groups.
The mortality rate rose steeply with age and was three times higher at one year for patients aged 85 and over compared to those who were under 60.
Professor David Clark, Head of the School of Interdisciplinary Studies at the University of Glasgow said: "Until now there has been a dearth of information on the proportion of the hospital population at any one time that is in the last year of life and therefore on how hospital policies and services can be oriented to their needs.
"We were able to link hospital records to death registrations to get an exact figure. One striking result was that 9% of patients in hospital at any one time will die on that admission."
The study was carried out to address the growing challenge of an ageing population and the need for more palliative and end of life care services and plans to advise families as to what to do as loved ones near the end of their lives.
The likelihood of dying in hospital varies across countries but is generally high.
One recent study ranked Scotland 12th out of 36 countries for the proportion of all deaths occurring in hospital (59%). Japan came top at 78%.
Professor Clark added: "In order for appropriate plans to be made, there is a need for hospitals to be aware of the figures from this report and to adopt a more vigorous approach to identifying patients who are entering the last year of their lives."