To determine whether leptin in patients with CAP acts as a nutritional or as an inflammatory marker and whether leptin plays any role regarding survival, we included 222 patients diagnosed of CAP, 142 men and 80 women, median age 74 years. We did not find significant differences in serum leptin levels between CAP patients and healthy controls, even after adjusting by BMI. Serum leptin levels were directly related with BMI, body fat and muscle mass and inversely related with inflammatory markers, including pro- and anti-inflammatory cytokines. Patients with positive blood cultures showed lower serum leptin and raised inflammatory markers. Although patients who died showed lower values of serum leptin, multivariate analysis showed that the prognostic value of low serum leptin levels depends on impaired nutritional status. In conclusion, we suggest that in CAP patients, leptin does not act as an inflammatory reactant but as a nutritional marker.