Although elderly patients who are admitted to hospital for any disease have a higher risk of pneumonia subsequently, whether those treated in hospital for pneumonia are at even greater risk is unknown. Therefore we retrospectively assessed morbidity and mortality due to pneumonia after discharge in 573 consecutive patients admitted to hospital for pneumonia, gastrointestinal infection, renal infection, or erysipelas. Average follow-up was 34 months. The incidence rate for pneumonia was 5.45 times higher in the group of patients discharged after pneumonia than in the other groups combined (95% confidence interval 2.89-10.26; p less than 0.001), and this group also had more deaths due to pneumonia (p = 0.06). For patients 50 years or older Streptococcus pneumoniae is the main cause of pneumonia. Pneumococcal vaccination after hospital treatment for an episode of pneumonia might be a cost-effective means of preventing disease in this group.