Objective: We recently reported that apolipoprotein CI (apoCI) protects against the development of murine bacterial sepsis. We now examined the time course of plasma apoCI levels in survivors and non-survivors of severe sepsis. Design: Prospective study in patients meeting predefined criteria for severe sepsis. Setting: University hospital intensive care unit. Patients and participants: Seventeen patients with severe sepsis. Interventions: In each patient, serial blood samples for determination of total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, apoCI, apoAI, apoB, and apoCIII protein as well as clinical outcome data were collected over 30 days. Measurements and results: Upon hospitalization, apoCI levels were approximately 5 times lower than normal values in septic patients, i.e. median 1.34 [interquartile range (IQR) 0.82-2.16] mg/dl. ApoCI gradually increased to median values of 5.51 (IQR 3.64-6.97) mg/dl on day 28. At day 0, apoCI levels tended to be lower in non-survivors than in survivors. Remarkably, apoCI levels remained low in non-survivors, whereas apoCI levels gradually increased to normal levels in survivors. This difference was significant and remained so after adjustment for lipoprotein core lipids. No such effect between survivors and non-survivors could be detected for lipoprotein lipids or for apoAI, apoB, and apoCIII after lipid adjustment. Conclusions: Plasma apoCI levels are markedly decreased in patients with severe sepsis. ApoCI levels were higher in survivors, even after adjustment for lipid levels, and recovered progressively to normal levels. In contrast, apoCI levels remained low in non-survivors. Therefore, a high plasma apoCI level predicts survival in patients with severe sepsis. © 2008 Springer-Verlag.