Through a house-to-house survey, 1325 people aged 11+ years registered at 2 primary health care centres (1 at high altitude and 1 at sea level) in Asir region, Saudi Arabia, were interviewed and examined for weight, height and peak expiratory flow rate. The prevalence of bronchial asthma at sea level (19.5%) was significantly higher than at high altitude (6.9%). Illiteracy, low income, use of coal and wood for heating, having a mud or tent house, lack of electricity inside dwellings and presence of sheep were also significant risk factors for bronchial asthma. In multivariate logistic regression, only altitude was found to be significantly associated with bronchial asthma (adjusted odds ratio = 3.94).