The aim of this study is to describe the changes in the aetiology of hospitalised patients with community-acquired pneumonia (CAP) during an 11-year observational period in a limited geographic area. Eight hundred and one (801) adult patients with CAP hospitalised were included. The patients were divided into three groups according to the time of presentation. Comprehensive microbiological laboratory tests were performed and differences in aetiology were analysed. In 228 patients (31%), a pathogen was detected, with Coxiella burnetii being the most common (20.1%). Significant variations in the prevalence of Chlamydophila pneumoniae were found between groups but not in other pathogens. In conclusion, long-term epidemiological studies may contribute to the knowledge of actual CAP aetiology.