Objectives: Total white blood cells (WBCs) decrease slightly in the elderly. In response to an acute infection, the number of WBCs increases and in sepsis, the increase is very dramatic. There are some reports about the effects of increased number of WBCs as a predisposing factor of bacteremia. An association between neutrophilia and eucopenia and increased mortality rate in the elderly has also been observed. We compared peripheral WBC counts in young and elderly patients with sepsis. Methods: A case-control study was carried out on 130 admitted patients who were divided into two groups based on age, ≥ 65 years (case group) and < 65 years (control group). All patients were hospitalized with the diagnosis of sepsis in two teaching hospitals in Tehran, Iran, 2001-2006. Results: Mean WBC counts at admission time were 17061.5 ± 14240.2 /μl in the case group and 13567.7 ± 9888.0 /ml in the control group. There were statistically significant associations between age and history of infection and history of hospitalization during the last month in the case group and also between age and source of infection (P < 0.05). Conclusions: The history of infection and the history of hospitalization during the last month with sepsis are important risk factors in elders.