Background and Aim: Infection is a common problem in intensive care medicine and many patients are treated aggressively and empirically with broad-spectrum antibiotics. Meningitis may be missed in intensive care unit (ICU) because some of these patients have fever and altered mental status from another illness and may be treated with impression of sepsis. In order to identify undiagnosed meningitis in ICU admitted patients, postmortem CSF analysis was performed immediately after death. Subjects and Methods: During 1 year, 43 patients underwent lumbar puncture after death. Samples were collected and analysis for cells, sugar and protein concentrations were obtained. Demographic characteristics and diagnosis of the patients were recorded and data analysis was performed by SPSS version 11.5. Results: CSF was completely normal in 62.8% of the patients and it was compatible with meningitis in two of them. Both of them had admitted with impression of sepsis and had another source of infection. Considering a subgroup of the patients who admitted to ICU with impression of sepsis, they were statistically significant. There was no significant difference between surgical and nonsurgical patients. Conclusions: Our findings suggest that meningitis may be missed in ICUs, and more liberal use of CSF analysis should be considered in critically ill patients, especially those who referred with impression of sepsis.