objectives: absence of one pulmonary artery is an uncommon congenital heart defect (chd). Most of these patients have associated cardiac defects. Early diagnosis and surgical intervention may prevent irreversible pulmonary hypertension and collateral formation. methods: a cross sectional descriptive study was done on records of 18 patients with absence of one pulmonary artery in Imam Reza Hospital of Mashhad University of medical sciences (a tertiary referral hospital) from 2001 to 2006. Data of history, physical examination, chest x-ray (cxr), cardiac catheterization and angiography reviewed and analyzed statistically. Results: Among 18 patients, 13 (72.2%) were male. The mean age of patients on diagnosis was 11.8±10.8 years (range 1-38 years). all patients had associated congenital heart defects except one. Most of these abnormalities were complex chd and tetralogy of fallot was the most common chd (7 cases). seventeen (77.8%) of patients had occult left pulmonary artery (lpa). cxr in all patients showed heart and mediastinum deviation toward the absent pulmonary artery. Conclusion: Early diagnosis and surgical intervention may allow growth of the pulmonary artery and prevent collateral formation and irreversible pulmonary hypertension. So complete evaluations for absence of pulmonary artery branch especially infants with CHD who are clinically suspicious is mandatory.this subjects also is suitable for pannel discussion.