Retrospective study of 26 radioclinical cases of mediastinal cystic lesions, realized betweenJanuary 2011 and December 2015 in the radiology department of the UHC Hassan II of Fez.All patients were examined by a chest X-ray (face and profile), a CT scan, and an ultrasoundinafew cases. The patients of our series were distributed as follows: Tumor and malformative origin (cysticlymphangioma in 6 cases, thymic cyst in 4 cases, bronchogenic cyst in 3 cases and pleuro-pericardialcystin2cases),infectiousorigin(hydatidcystin5cases,mediastinalabscessin4cases,Tuberculosisin2cases).Theimageryallowedtoeasilyconfirmtheliquidnatureof thesemasses.Theetiologiesareveryvariedandthediagnosticorientationisbasedessentially onthe topography andtheage ofthe patient.