Pericardial cyst are rare, most of them congenital in origin. They usually are located in the cardiophrenic angles, mainly on the right side. Although the most frequent clinical presentation is asymptomatic, and the prognosis is benign, important complications had been described. For this reason we used to take aggressive therapeutic interventions like percutaneous aspiration or surgical resection by thoracotomia or thoracoscopy. The case we report is interesting because it was an atypically located left upper paramediastinal cyst, and not congenital in origin but posttraumatic. The diagnosis was made by imaging techniques and we accomplished conservative alternative because of the favourable evolution. We think that it should be a good option in case of asymptomatic and no complicated cases.