Background. Diaphragmatic mesothelial cysts are congenital lesions that derive from coelomic remnants. Objective. To describe their radiological appearance on US, CT and MRI. Materials and methods. Four children (aged 714years) who underwent surgery and for whom there was pathological confirmation of the diagnosis. Five more children (012months old) who were managed conservatively, but for whom there was a high degree of suspicion for this diagnosis. Results. All lesions presented as a cystic mass between the thoracic wall and the liver, in the right posterolateral costophrenic angle. Some lesions showed subtle evidence of their extrahepatic location. Conclusions. The radiological findings identified are highly suggestive of diaphragmatic mesothelial cyst.