53 patients with community-acquired pneumonia requiring treatment in an Intensive Care Unit (ICU) were studied retrospectively. The majority of patients (77%) had some predisposing factor: illness, smoking or alcoholism. A cause of pneumonia was established in 53% of the cases; Streptococcus pneumoniae was the dominating pathogen. Immediate active treatment was required in 70% of the patients and 58% were treated with mechanical ventilation. The overall mortality was 25% (32% among patients treated with mechanical ventilation) and rose to 39% when a follow-up period of 3.25 years on average was included. A significantly higher mortality rate was seen among elderly patients and among those who were previously immunocompromised or who had a leukocyte count of less than or equal to 9 X 10(9)/l on admission to hospital. It is concluded that although the mortality rate was considerable among the 53 ICU-treated patients with severe community-acquired pneumonias, several were saved by intensive care treatment. Most of those who survived their pneumonia eventually recovered fully.