Objective - To assess physicians' current adherence to the Norwegian clinical guidelines for the treatment of hypertension. Design - Descriptive, retrospective registration of information front patient records of one specified year. In addition, mailed questionnaire to examine the representativeness of the participating doctors. Setting - General practice in Sor- and Nord-Trondelag counties in Norway, 380 000 inhabitants. Patients - In one year 2468 patients were registered with the diagnosis of hypertension in the records of 56 general practitioners. The patients were 57% women and 43% men; 41% were 70 years or older. Main outcome measures - Levels of blood pressure in accordance with the recommendations of the Norwegian clinical guidelines far hypertension. Fractions of patients with a measured blood pressure and serum cholesterol in one year. Results - At least one blood pressure was recorded in 95% of the hypertensive patients during the specified year. The systolic blood pressure was 140 mmHg or less in 25% and 160 mmHg or less in (65%, while the diastolic blood pressure was 90 mmHg or less in 61%, According to the Norwegian clinical guidelines for systolic blood pressure, 29% of the women and 21% of the men were above recommended levels for treatment. With respect to the diastolic blood pressure, the figures were 38% for women and 40% for men. Patients under 60 years of age were often not treated according to the recommendations. Serum cholesterol was not recorded during the specified year in 68% of the total group, nor in 55% of patients aged 65 years or younger. Conclusion - There are still major discrepancies between current practice and the intentions laid down in the Norwegian clinical guidelines. A discussion of alternative methods for implementation and for evaluation of the efficacy of clinical guidelines is needed.