The ideal biomarker to assess response and prognostic assessment in the infected critically ill patient is still not available.The aims of our study were to analyze the association between early C-reactive protein kinetics and duration and appropriatenessof antibiotic therapy and its usefulness in predicting mortality in infected critically ill patients. We have carried out an observational retrospective study in a cohort of 60 patients with community-acquiredpneumonia, aspiration pneumonia and bacteremia at an intensive care unit. We have collected C-reactive protein consecutive serumlevels for eight days as well as duration and appropriateness of initial antibiotic therapy. C-reactive protein kinetic groups were definedbased on the levels at days 0, 4 and 7. With a follow-up of one year, we have evaluated mortality at different time-points. We have obtained three different C-reactive protein kinetic groups from the sample: fast response, delayed but fast responseand delayed and slow response. We did not find statistically significant associations between C-reactive protein kinetics and early (intensivecare unit, hospital and 28-days) or late (six months and one year) mortality and antibiotic therapy duration (p > 0.05). Althoughthere were no statistically significant differences between the appropriateness of antibiotic therapy and the defined groups (p = 0.265),no patient with inappropriate antibiotic therapy presented a fast response pattern. Several studies suggest the importance of this protein in infection. Early C-reactive protein kinetics is not associated with response and prognostic assessment in infected critically ill patients.Nevertheless, a fast response pattern tends to exclude initial inappropriate antibiotic therapy.