Background:In spite of recent advents, and novel improvements in the diagnosis and treatment of pulmonary tuberculosis (TB), definitive diagnosis of pulmonary TB in children is problematic. Therefore, measurement of the serum level of adenosine deaminase (ADA) was later introduced as a helpful marker for the diagnosis of TB. Objectives: The purpose of this study was to determine the usefulness of the ADA test in the diagnosis of pulmonary TB, and compare enzyme activity between patients with pulmonary TB and those with other pulmonary infections. The sampling strategy was randomized, and the design of study was case-control diagnostic descriptive, we used IBM SPSS V-16.0.2 software for analyzing our data. Patients and Methods: This study was performed at the National Research Institute of Tuberculosis and Lung Diseases (NRITLD) in Tehran, IR Iran. In all, 49 children, divided into 3 groups, were examined. Of these, 22 had pulmonary TB, 17 had other pulmonary infections, and the remaining 10 children were normal and were assigned to the control group. Results: Serum ADA levels were higher in the pulmonary TB patients than in the control group (P < 0.05), however, these levels did not differ significantly between TB patients and patients with other pulmonary infections (P = 0.391). Our evaluation revealed that ADA level in TB patients with a positive smear of gastric washing were higher than those in patients with a negative smear (P = 0.006). Conclusions: Similar to the other studies, this study showed higher serum ADA level in pulmonary TB patients than in normal individuals. However, ADA was not found to be a suitable marker for differentiating between pulmonary TB and other pulmonary infections.