In this prospective study 37 children (ranging 2 months-15 years) with acute pneumonia were evaluated by Doppler echocardiography for the presence of pulmonary hypertension (PH). The goal of this study was to determine the frequency of PH in children with acute pneumonia because the diagnosis of PH influenced the treatment of pneumonia in these patients. The patients who had more than 35 mmHg of systolic pulmonary arterial pressure were considered to have PH. In our study PH was found in 15 (40.5%) of 37 patients. We did not find any significant difference for the parameters including the age, weight, height, clinical symptoms and signs (fever, cough, dyspnea, tachycardia and tachypnea etc.), and laboratory findings such as hemoglobin, PCO2, HCO3 and PO2 between the patients with and without PH (p>0.05). However, there was a significant difference in cyanosis, cardiac failure, blood pH level and O2 saturation measured by pulse oximetry between the patients with and without PH (p<0.05).