Adrenal insufficiency is believed to occur frequently in severe sepsis and septic shock. The aim of the present study was to determine whether adrenal function is also related to the severity of community-acquired pneumonia (CAP). In total, 64 Japanese patients with CAP were consecutively enrolled in the present study, which was carried out during 2005-2006. Serum adrenocorticotropic hormone (ACTH) and cortisol were measured in each subject, as was the response of cortisol secretion when 250 mug of cosyntropin was administered. Analyses were performed comparing these values with the score calculated according to the Pneumonia Patient Outcomes Research Team (PORT) cohort study, the number of in-hospital deaths and the length of hospital stay. As the PORT score increased, serum ACTH and cortisol also increased, while the response of cortisol secretion to the administration of cosyntropin decreased. In the analysis by receiver operating characteristic curves, adrenal dysfunction was related significantly to both the number of in-hospital deaths and the length of hospital stay. Adrenal dysfunction was shown to correlate with the Pneumonia Patient Outcomes Research Team score and the clinical outcomes, while adrenal insufficiency defined by the cosyntropin stimulation test was rare in the present study.