Several studies have shown that C-reactive protein (CRP) is a marker of infection. The aim of this study was to evaluate CRP as marker of prognosis outcome in septic patients and to assess the correlation of CRP with severity of sepsis. During a 14-month period, we prospectively included all patients with sepsis admitted to an intensive care unit (ICU). Patients were categorized into sepsis, severe sepsis and septic shock. Acute Physiology and Chronic Health Evaluation (APACHE) II score, Simplified Acute Physiology Score (SAPS) II, Sequential Organ Failure Assessment (SOFA) score, CRP, body temperature and white cell count (WCC) of the day of sepsis diagnosis were collected. One hundred and fifty-eight consecutive septic patients (mean age 59 years, 98 men, ICU mortality 34%) were studied. The area under the receiver operating characteristics curves of APACHE II, SAPS II, SOFA, CRP, body temperature and WCC as prognostic markers of sepsis were 0.75 [95% confidence interval (CI) 0.67-0.83], 0.82 (95% CI 0.75-0.89), 0.8 (95% CI 0.72-0.88), 0.55 (95% CI 0.45-0.65), 0.48 (95% CI 0.38-0.58) and 0.46 (95% CI 0.35-0.56), respectively. In the subgroup of patients with documented sepsis we obtained similar results. The ICU mortality rate of septic patients with CRP < 10, 10-20, 20-30, 30-40 and > 40 mg/dL was 20, 34, 30.8, 42.3 and 39.1%, respectively (P = 0.7). No correlation was found between CRP concentrations and severity of sepsis. In septic patients, CRP of the day of sepsis diagnosis is not a good marker of prognosis.