A pilot study on the epidemiology of hypertension was carried out in 3 out of the 8 districts in the state of Selangor, namely Klang, Sabak Bernam and UIu Langat. stratified random sampling, 435 households were selected for the study. Eventually 312 (72%) households were surveyed: 963 (94%) out of the 1,030 persons aged 15 years and above living in the selected households were interviewed, and 957 of them were examined. The mean age of the respondents was 33 years. Taking a systolic pressure of more than 140 mmHg and/or diastolic pressure of more than 90 mmHg as hypertension, 1 in every 7 of those equal and mor.e than 15 years of age had hypertension, i.e. 140/0. 5.40/0 had a systolic pressure of equal and more than 160 mmHg, and 4.7% had a diastolic pressure of equal and more than 95 mmHg. The study showed that there was a significant rise in the prevalence rates with age in both sexes. There was no significant difference in the prevalence rates among. the sexes, ethnic groups (Malays, Chinese and Indians) and urban and rural areas. The mean systolic pressure ranged from 112-147 mmHg and diastolic from 69 - 73 mmHg. Hypertension was significantly more common among smokers (18.1%) than nonsmokers. There was no significant relationship between hypertension and tea, coffee and alcohol consumption. Hypertension was significantly more common among those with no physical activity (34.8%) as compared with those with physical activity (13.5%). 67% of the hypertensives were aware of their illness but only 36.1% of them were under treatment.