Pneumonia is a major direct cause of death in the elderly. Although aspiration based on a reduced cough reflex is one of the causes of pneumonia in the elderly, there are few studies of angiotensin-I converting enzyme inhibitors (ACE inhibitors), which are antihypertensive drugs that induce cough, as a factor influencing the incidence of pneumonia in institutionalized elderly subjects. To assess the effect of ACE inhibitors and dihydropiridine calcium-channel blockers on the incidence of pneumonia, we conducted a hospital-based case-control study. Cases were 55 pneumonia patients aged > or = 65 years during a 1-year period. The controls were elderly subjects, frequency matched to the cases by age and gender (n = 220). Data were collected on known risk factors and on medication for hypertension, consisting of ACE inhibitors, calcium-channel blockers, and nonantihypertensive medication. The significance of differences in risk factors was analyzed using univariate and multivariate comparisons of cases and controls. After adjustment for potential confounding factors, the relative risk estimates for pneumonia were 0.38 (95% confidence interval [CI], 0.15-0.97) and 1.84 (95% CI, 0.89-3.78) for ACE inhibitors and calcium-channel blockers, respectively, relative to nonantihypertensive medication. The preventive effect of ACE inhibitors on pneumonia was apparent in long-acting ACE inhibitor users (0.24; 95% CI, 0.07-0.88). We conclude that ACE inhibitor use is an independent factor reducing risk of pneumonia among elderly inpatients.