BACKGROUND: Lymphocytopenia is a common finding in critically ill patients while lymphocyte depletion in critically ill patients is presumed to have little clinical significance. However, a total lymphocyte count has been reported to provide prognostic information in surgical patients. The aim of this study was to evaluate the association of a total lymphocyte count (TLC) with a prognostic criterion in critically ill patients. METHODS: The patients were divided into three groups according to their TLC on admission to intensive care unit (ICU) (Group 1: TLC > 1.0 x 10(9)/L, Group 2: 0.7 x 10(9)/L < TLC < 1.0 x 10(9)/L, and Group 3: TLC <0.7 x 10(9)/L). Outcomes examined were patients' in-hospital mortality, length of hospital stay and incidence of infection. RESULTS: Patients with a TLC less than 0.7 x 10(9)/L (Group 3) had an infection twice (32% VS 15%) as often as those with a TLC more than 0.7 109/L (Group 1 2). But, in the hospital stay and mortality, there was no significant difference among the groups. CONCLUSIONS: TLC is very useful indicator in critically ill patients with a high risk of hospital infection on ICU admission.