And less than half of those who were aware that they had hypertension had managed to bring the problem under control, the study found.
People with high blood pressure, also called hypertension, have an increased risk of developing heart disease, stroke, kidney disease and dementia, previous research has shown.
Scientists examined 1,604 persons from southwest London, Limburg in Belgium and Abruzzo in Italy. The subjects also answered questions about healthcare and lifestyle habits.
The study found that 24 percent of participants had high blood pressure, but than only 44 percent of them were aware of their condition.
Of those, less than half had reduced their pressure under a widely-used benchmark of health used in testing, 140 over 80 mm of mercury.
High blood pressure is defined by the World Health Organisation (WHO) as being 140 over 90 mm of mercury or more. Mercury is used in blood-pressure gauges.
The first number measures maximum heart pressure (systolic), while the second measures pressure when the heart is in a resting phase (diastolic).
"Our results show that high blood pressure is a looming problem for Europe," said Franco Cappuccio, a research at Warwick Medical School in Britain, and leader of the British arm of the study.
Management of the problem is better in Britain that in many other European countries, in part because doctors have incentives to help patients reach blood pressure targets, he said.
"But we still have too many patients not adequately treated, and the incidence of hypertension is still rising."
The study was published in the International Society of Hypertension's Journal of Hypertension.