Detecting hypertension: screening versus case finding in Norway. OBJECTIVE--Evaluation of detection of hypertension in adults in the county of Nord-Trondelag, Norway. DESIGN--Cross sectional survey with clinical follow up examinations. SETTING--Health survey by screening teams from the national health screening service, and examinations by all 106 general practitioners in the county. SUBJECTS--During 1984-6, 74,977 persons (88.1% of those aged 20 years and over) participated in the health survey. MAIN OUTCOME MEASURES--Hypertension (when assessed by standardised recording and by questionnaires on drug treatment for hypertension) according to the blood pressure thresholds used in the Norwegian treatment programme. Subjects positive on screening were grouped after clinical examination into treatment groups. RESULTS--In all, 2399 subjects were positive for hypertension. Before screening 6210 (8.3%) patients reported taking antihypertensive drugs and another 3849 (5.1%) had their blood pressure monitored regularly. All who screened positive were referred to their general practitioner and evaluated according to a standard programme. As a result, drug treatment was started in 406 (0.5%) participants screened and blood pressure monitoring in another 1007 (1.3%). Of all patients taking antihypertensive drugs after the screening, 6399 (94.0%) had been diagnosed before screening, and of those whose blood pressure was monitored after the screening, 79.3% had been diagnosed before screening. CONCLUSIONS--At the blood pressure screening thresholds used, and when hypertension is defined by an overall clinical diagnosis, the results indicate that general practitioners can find and diagnose hypertensive patients with the case finding strategy. 