Only a small proportion of patients with arterial hypertension are adequately treated. Although a possible cause for this fact may be the deficient knowledge of physicians about diagnosis and treatment of arterial hypertension, to date no studies have addressed this important problem in Germany. Therefore, we have reviewed the knowledge of internists and general practitioners about diagnosis and treatment of arterial hypertension using a questionnaire. The guidelines of the German Hypertension Society were used as the reference standard. The questionnaire was sent out in December 1999 to all internists (n = 15,952) and to a random sample of general practitioners (n = 8947) who work as statutory health insurance physicians. A total of 11,547 questionnaires were sent back and could be analysed. Adequate guideline knowledge was assumed if five out of eight questions were correctly answered; the correct answers had to include the correct definition of arterial hypertension (140/90 mmHg). The correct definition of arterial hypertension was known by 4103/11,547 participants (36%). An adequate guideline knowledge was found in 18.8% of the general practitioners and in 26.6% of the internists. There were no relevant regional differences. The level of awareness about diagnosis and treatment of arterial hypertension is insufficient among internists and general practitioners. This insufficient knowledge may in part explain the inadequate care for patients with arterial hypertension. Thus, the implementation and evaluation of new information and training strategies are mandatory to improve the care for patients with arterial hypertension.