The objective of this case-control study was to identify the main risk factors for community-acquired pneumonia (CAP) in a German adult population. A self-administered questionnaire was given to CAP cases provided by the German competence network CAPNETZ and population-based, randomly selected controls (sex- and age-matched). Multivariate analysis showed that in addition to known risk factors such as previous CAP [odds ratio (OR) 1·6, 95% confidence interval (CI) 1·3–2·1], more than one respiratory infection during the previous year (OR 3·6, 95% CI 2·9–4·5), chronic pulmonary diseases (OR 2·3, 95% CI 1·7–3·0), number of comorbidities (OR 1·6, 95% CI 1·4–1·9), and number of children in the household (2 children: OR 2·2, 95% CI 1·5–3·4; ⩾3 children: OR 3·2, 95% CI 1·5–7·0) were independent risk factors for CAP. This was pronounced in particular in people aged ⩽65 years. The most likely explanation for this finding is higher exposure to infectious agents.