Severe pneumonia is a major cause of mortality in children. The present study evaluated the diagnostic value of serum C-reactive protein (CRP) levels for cases of severe pneumonia. A total of 862 children, hospitalized for acute respiratory tract infections, were evaluated between September 2008 and February 2011; the serum levels of CRP were measured in all the children. Bacterial identification was performed, while polymerase chain reaction was used to detect the 12 respiratory viruses. Multivariate logistic regression analysis was performed with independent [CRP, proportion of neutrophils (NEUT), body temperature, sputum production, age and dyspnea] and dependent (severe and mild pneumonia) variables for clinical diagnosis, which produced three new variables that represented an individual's predictive value: Pre-1, Pre-2 and Pre-3. A receiver operating characteristic (ROC) curve was generated using the new variables to assess their predictive value for severe pneumonia. Of the 862 patients, 108 individuals were diagnosed with severe pneumonia and 754 individuals had mild pneumonia. Increased levels of CRP were associated with severe pneumonia and bacterial infection (P<0.05). Multivariate logistic regression analysis found that severe pneumonia was associated with the levels of CRP, body temperature, expectoration, age, NEUT and dyspnea (P<0.05). The ROC curve of the regression diagnostics model sequentially presented CRP, CRP and the other five correlative variables (NEUT + body temperature + sputum production + age + dyspnea) and the other five correlative variables used to diagnose severe pneumonia. The area under curve values were determined as 0.550 for Pre-1 [95% confidence interval (CI), 0.490–0.609], 0.897 for Pre-2 (95% CI, 0.861–0.932) and 0.893 for Pre-3 (95% CI, 0.855–0.931). The results revealed that the six correlative variables had improved accuracy in the diagnosis of severe pneumonia. The serum levels of CRP were strongly associated with bacterial infection and severe pneumonia. Therefore, the CRP level, along with other parameters, may be used as early indicators of severe pneumonia development. However, the efficiency of the CRP level alone to diagnose severe pneumonia was found to be limited.