Introduction: Multi-detector pulmonary CT angiography and high resolution CT are now play an important role in diagnosis of pulmonary hypertension and are considered the first line of investigation in the diagnosis of most of the pulmonary vascular and interstitial disorders that’s cause pulmonary hypertension. Purpose: The aim of this study is to evaluate the role of Multi-detector pulmonary CT angiography and high resolution CT in the diagnosis of pulmonary hypertension, its causes and complications. Patients and methods: 100 patients (diagnosed either clinically or by echocardiography to have pulmonary hypertension) were examined using a 4-multidetector CT scanner in the radiology department in Cairo University. The study population was assisted for different MDCT signs of pulmonary hypertension, lung parenchyma, vascular and cardiac findings that help in the diagnosis of different causes of pulmonary hypertension and complications occurred due to pulmonary hypertension. Results: In all cases the main pulmonary artery was larger than 29 mm and further divided according to the size into three groups (< 35 mm= 54%, ≥ 35≤ 40 mm= 28%, > 40 mm= 18%). The more than 1:1 relation between segmental pulmonary artery and the bronchus in different pulmonary lobes was seen in 88% of cases. The more than 1:1 relation between the main pulmonary artery and the aorta was seen in 76% of cases. According to the other CT findings, the causes were divided into four groups. Group A (pulmonary) 36%, Group B (cardiac) 27%, Group C (vascular) 17% and Group D (idiopathic) 20%. The cardiac complications were seen in 47% of the cases. Conclusion: Multi-detector pulmonary CT angiography and high resolution CT are a relatively available, minimally invasive investigation that can now be considered as important modality that show signs of pulmonary hypertension and the first line of investigation in diagnosis possible causes of pulmonary hypertension as pulmonary vascular disorders (e.g. pulmonary embolism) and interstitial lung disease (e.g. idiopathic pulmonary fibrosis).