Background: Attention deficit hyperactivity disorder (ADHD) etiology is not completely understood, but common comorbid dysfunction of immune system suggest that these systems may be affected by common genetic background and molecular mechanism, for example, increase levels of specific cytokines are observed in ADHD. The aim of this study was to evaluate the level of inerleukin-2 (IL-2) as a biomarker of ADHD and find out the relation between interleukin-2 and ADHD symptoms. Patients and Methods: A case control study carried out on 90 children who assigned into two equal groups: ADHD patients: met diagnosis of ADHD according to DSM V criteria and a control group. All groups were subjected to full history taken, thorough clinical examination , and measurement of Human IL-2 by ELISA technique. Results: The mean value of IL2 level was statistically significantly higher among ADHD cases than control group (p < 0.001). There was statistically significant positive correlation between IL2 level (ng/L) and Duration Of illness and Conner Parent Scale, there was statistically significant negative correlation between IL2 level (ng/L) and IQ level. While there was statistically nonsignificant correlation between IL2 level (ng/L) and age and Order of ADHD child among his siblings. Conclusion: Serum IL-2 levels were elevated in ADHD children and correlated with the severity of ADHD .