Introduction: Hypertrophied tonsils and adenoids may cause upper airway obstruction and cardio-pulmonary complications due to pulmonary arterial hypertension. The aim of this study was to determine the correlation between mean pulmonary arterial pressure (mPAP) and selected adenotonsilar hypertrophy indexes. Materials and Methods: Thirty two patients with upper-airway obstruction resulting from hypertrophied tonsils and adenoids were included in our study. Mean pulmonary arterial pressure was measured by a non-invasive method using color doppler echocardiography. Upper airway obstruction was evaluated by clinical OSA (obstructive sleep apnea) scoring and also adenoidal-nasopharyngeal (A/N) ratio in the lateral neck radiography. Results: Fifty percent of the patients with a normal OSA score, 20% of those with a suspected OSA score and also 50% of cases with OSA had pulmonary hypertension (mPAP>20mmHg) which was not statistically significant (P=0.198). Mean Adenoidal-nasopharyngeal ratio in patients with a normal mPAP (mPAP≤20mmHg) was 0.61±0.048 and it was 0.75±0.09 in those with pulmonary hypertension; the difference was statistically significant (P=0.016). Conclusion: It seems that A/N ratio could be used as a predicting factor for increased mPAP in children with upper airway obstruction and a pediatric cardiologist consultation may be necessary before some surgical interventions.