In order to investigate the predisposing conditions and aetiologic agents in patients with recurrent pneumonia, we prospectively studied 653 immunocompetent patients, 50-85 years of age, who had been treated in hospital for community-acquired pneumonia. After an average patient follow-up period of 32 months, 11 variables were examined for association with the following end points: death, recurrence of pneumonia and recurrence of pneumococcal pneumonia. During the follow-up period there were 171 episodes of pneumonia in 115 of the 653 patients, and 52 deaths (all causes). Multivariate analysis showed that age, male sex, congestive heart failure and presence of other chronic diseases were significantly associated with higher mortality. Age and chronic pulmonary disease were associated with recurrence of pneumonia. The major aetiologic agents were Streptococcus pneumoniae (26%), Haemophilus influenzae (11%) and Moraxella catarrhalis (6%). We conclude that pneumonia recurrences are common in middle-aged and elderly patients after treatment in hospital for community-acquired pneumonia. The recurrence risk is higher in elderly patients, and in those with chronic pulmonary diseases. Given the prominence of H. influenzae and M. catarrhalis found in the present study, these organisms should always be considered when choosing the initial antibiotic in patients with recurrent pneumonia.