As humans age their ability to combat infections declines as a result of an age-related loss of immune status. We have shown that the ability of neutrophils to ingest E.coli is reduced in healthy elderly humans and here we report the effects of a common trauma, hip-fracture, on infection susceptibility and neutrophil function in elderly humans. 44 elderly patients (mean age 82.5 years) with a hip-fracture and 9 young subjects (mean age 25.9 years) with a single limb fracture were recruited to the study. Blood was taken at the time of injury and 5 weeks later and infections were monitored throughout. 47.8% of the elderly developed an infection, with a predominance of chest and urinary tract infections. No infections were seen in the young cohort. At the time of trauma neutrophil phagocytic ability was the same in both age groups, whereas superoxide generation in response to fMLP was significantly reduced in the elderly group. 5 weeks after trauma superoxide generation remained low and phagocytic ability was also significantly reduced in the elderly patients. In addition the serum ratio of the immune suppressing corticosteroid cortisol, to the immune enhancing steroid dehydroepiandosterone (DHEA), was raised 3 fold in the elderly trauma patients compared to healthy elderly controls. In vitro studies revealed that cortisol depressed neutrophil superoxide generation whereas DHEA enhanced this bactericidal response. We propose that response to trauma in the elderly involves suppression of neutrophil function by an altered cortisol:DHEA ratio, influencing susceptibility to infections.