Influenza in children may mimic other infections leading to insufficient treatment. Determination of parameters that facilitate diagnosis and indicate severity would be useful to optimize treatment modalities. We prospectively screened 432 children for influenza infection. Forty-six children at the age of 4 weeks to 14 years (median, 18 months) with confirmed influenza A infection were analyzed. A clinical score of illness severity was calculated from the symptoms presented. To evaluate the dependency of the clinical score on C-reactive protein value, leukocyte count, age, and days of hospitalization, correlation and regression analyses were carried out. Neither the C-reactive protein values (median, 0.85 mg/dL; range, 0.2-18.6; r=0.14; p=0.35) nor the leukocyte counts (median, 7.95 G/L; range, 3.5-17.6; r=-0.14, p=0.34) correlated significantly with the clinical score of influenza severity. Thus, in daily clinical practice, C-reactive protein and leukocytes seem to be insufficient parameters to describe the clinical severity of influenza A infection in children.