The quality of the control of hypertension has been assessed in 18 European population groups, in a multicentre cooperative project. Five approaches were taken: epidemiological survey, clinical evaluation of samples of patient records, assessment of patient satisfaction, exploration of physicians' attitudes and knowledge, and drug utilisation studies. The participating centres could choose any or all of the above approaches; a total of 31 subprojects was carried out. Undiagnosed hypertension varied in different centres from 17% to 34% of all hypertension, and not more than 29% of all treated hypertensive patients had attained normal BP. Diuretics were the most commonly prescribed drugs, followed by beta-blockers. Although physicians expressed their concern about other cardiovascular risk factors and declared that they considered nonpharmacological treatment important, the findings in the patient survey did not confirm such attitudes. Finally, an analysis of patient satisfaction showed a mixed pattern. In conclusion, the control of hypertension in populations, through detection and treatment, as well as patient education and physician information, was studied.