The mortality rate in critically ill patients with pneumonia who require invasive vital organ support, including mechanical ventilation, in an intensive care unit (ICU) remains above 50%. The contribution of these costly life support systems to the survival of patients with extensive pneumonia is a matter for debate. The high mortality rate in this group of patients can be attributed in part to the fact that they are frequently referred for ICU care when their condition has already deteriorated to the point of no return. A retrospective study over 18 months of 34 cases of community-acquired pneumonia (17 patients required ventilatory support in the respiratory ICU) was undertaken to identify criteria which would justify early admission to an ICU. These were first-line clinical and biochemical factors, three of which were present in all patients on admission to hospital: (i) bronchopneumonia or lobar pneumonia involving more than two lobes (P less than 0.001); (ii) respiratory rate greater than 30/min (P less than 0.001); and (iii) partial arterial oxygen pressure less than 8 kPa (P less than 0.001). Other systemic factors associated with a poor prognosis and admission to the ICU were clinical signs of septicaemia, abnormal liver function and low serum albumin value. A scoring system for severity of pneumonia based on these factors is proposed. The possibility of an improved prognosis in a potentially reversible disease can become a reality if this approach is employed prospectively.