PURPOSE: An oblique interface in the right cardiophrenic angle, extending superomedially from rightretrocardiac or supradiaphragmatic region inferolaterally to peridiaphragmatic region, is occasionally observed onposteroanterior chest radiograph. The aim of this study was to evaluate the frequency of visualization of the interface on chest radiographs and to elucidate its nature on radiographic-CT correlation. MATERIALS AND METHODS: Posteroanterior chest radiographs from 300 consecutive subjects were analyzed to evaluate the frequency and demographic data about an oblique interface in the right cardiophrenic angle. Thin-section CT scans(1-mmcollimation and 5-mm intervals) were obtained from the subjects with positive interface on chest radiograph for assessment of the nature of the interface. The demographic data in the subjects with and without the interface were tested statistically to note any difference between two groups. RESULTS: Oblique interface in the right cardiophrenic angle was present in 29 subjects(9.7%) on chest radiograph. The age of the subjects with positive interface(13 men and 16 women) ranged from 19 to 70 years(mean ±SD, 47± 12.7 years) whereas the age of the subijects without the interface from 16 to 82 years (mean ±SD, 50±9.1 years)(p>0.1). The body weight of the subjects with the interface ranged from 41 to 72 Kg(mean ±SD, 60 ± 8.0Kg) whereas the body weight of the subjects without the interface from 41 to 85 Kg(mean ±SD, 63±10.1Kg)(p>0.1). On CT scan, it was formed due tocontact between the epipericardial fat and the right middle lobe of the lung in 27 subjects(93%) and between the inferior vena cava and the medial basal segment of the right lower lobe of the lung in two(7%). CONCLUSION: Oblique interface in the right cardiophrenic angle is occasionally visualized on chest radiograph. It is formed due to contact between the right middle lobe of the lung and pericardial fat in most cases. The frequency of visualization of the interface has no relationship to age and body weight of the subjects.