This study was conducted on 80 children, 30 had congenital heart diseases (CHD) with pulmonary hyper tension (PH) (group I), they were divided into mild pulmonary hypertension subgroup (31-49mmHg) (n = 15) and moderate or severe pulmonary hypertension subgroup, pulmonary artery systolic pressure (PASP) > or = 50 mmHg (n = 15), 30 had congenital heart diseases without pulmonary hypertension (group II) while group III included 20 apparently normal children as control group. All cases were subjected to full medical history, clinical examination, chest & heart X- ray, ECG and Echocardiography. Plasma adrenomedulin (AM) level was measured by radioimmunoassay technique. The results showed significant increase in the plasma adrenomedullin level in group I than group II & III, (P < 0.001). It was significantly elevated in moderate or severe - PH subgroup as compared to mild -PH subgroup (P<0.01). Moreover there was significant increase in plasma adrenomedullin level in group II than group HI, (p < 0.001). Also the results showed significant positive correlation between adrenomedullin & pulmonary artery pressure (PAP) in all studied groups. Correlation coefficient "r" in group I, II & III was 0.980, 0.880 & 0.877 respectively & p value was < 0.001 in all groups. From this study it was concluded that the plasma adrenomedullin may be used as a marker for right ventricular deterioration, during the progression of PH in the cases of CHD, plasma AM may play an important role in the development of PH. The increased AM may represent a compensatory mechanism. AM may be involved in the defence mechanism against further increase of pulmonary arterial pressure. AM could be used as a reliable indicator of the severity of CHD associated PH.