OBJECTIVE: To assess whether passive smoking exposure at home is a risk factor for community-acquired pneumonia (CAP) in adults. SETTING: A population-based case-control study was designed in a Mediterranean area with 860 000 inhabitants >14 years of age. PARTICIPANTS: 1003 participants who had never smoked were recruited. PRIMARY AND SECONDARY OUTCOME MEASURES: Risk factors for CAP, including home exposure to passive smoking, were registered. All new cases of CAP in a well-defined population were consecutively recruited during a 12-month period. METHODS: A population-based case-control study was designed to assess risk factors for CAP, including home exposure to passive smoking. All new cases of CAP in a well-defined population were consecutively recruited during a 12-month period. The subgroup of never smokers was selected for the present analysis. RESULTS: The study sample included 471 patients with CAP and 532 controls who had never smoked. The annual incidence of CAP was estimated to be 1.14 cases×10(-3) inhabitants in passive smokers and 0.90×10(-3) in non-passive smokers (risk ratio (RR) 1.26; 95% CI 1.02 to 1.55) in the whole sample. In participants ≥65 years of age, this incidence was 2.50×10(-3) in passive smokers and 1.69×10(-3) in non-passive smokers (RR 1.48, 95% CI 1.08 to 2.03). In this last age group, the percentage of passive smokers in cases and controls was 26% and 18.1%, respectively (p=0.039), with a crude OR of 1.59 (95% CI 1.02 to 2.38) and an adjusted (by age and sex) OR of 1.56 (95% CI 1.00 to 2.45). CONCLUSIONS: Passive smoking at home is a risk factor for CAP in older adults (65 years or more).