For the treatment for pulmonary hypertension (PH), the differential diagnosis of its causal diseases is essential. To determine whether X-ray CT is useful for differentiating PH, we reviewed CT findings of 53 patients (18 men and 35 women, mean age of 44.9) given a diagnosis of PH, consisting of 25 with primary pulmonary hypertension (PPH), 18 with chronic pulmonary embolism (cPE), 6 with Eisenmenger syndrome, 5 cases of collagen diseases, 2 of acute PE, and 1 of cor pulmonale. The intrapulmonary distribution of CT findings (ground glass opacity [GGO], mosaic attenuation, striation and/or infiltration, and interlobular septal thickening) were reviewed and scored on a 4-point scale (grade 0: no findings, 1: involving one third of the lung, 2: involving one-two thirds, and 3: diffuse distribution) by two radiologists who reached a consensus. PPH showed preferentially diffuse distribution of GGO as compared with cPE (p<0.05). However, there was no apparent relationship between the pulmonary vascular resistance and the distribution of GGO in PPH cases. The mosaic attenuation pattern was more frequent in cPE (43%) than PPH (12%; p<0.05). Striation and/or infiltration was observed in 36% of cPE, but only 4% of PPH. Interlobular septal thickening was seen in 16% of PPH, and 0% in cPE. Evaluation of CT findings is useful to differentiate PH.