Abstract： Objective　To analyse the CT findings of Bochdalek hernia in adult.Methods　The CT scan of 42 cases were reviewed showing a mass abutting the upper surface of the diaphragm, the defect was located in the posteromedial aspect of hemidiaphragm with continuity of subdiaphragmatic and supradiaphramatic densities through the diaphramatic defect. Among these, 25 cases were male and 17 cases female. The average age was 64 years, 71.4%≥60 old.Results　53 Bochdalek hernias were identified in 42 cases, 11 cases were bilateral, 21 cases were on the left and 10 cases were on the right side. The diaphragmatic defects diameter ranged 0.5～6.7 cm, the median was 2.8 cm. The range of Bochdalek hernias diameter was 1.5～9.0 cm, with median of 3.7 cm. There was a significant association between diaphragmatic defects and size of hernias (rs=0.72,P＜0.01). Chronic pulmonary disease was detected in 91% patients during CT scans.Conclusion　Adult Bochdalek hernia is not a rare condition, CT scan can accurately identify the location, size of diaphragmatic defect and content of hernia. The age and chronic pulmonary disease play an important role in the formation of this hernia.