Thymic cysts of the mediastinum are uncommon lesions which are generally located at the anterior mediastinum. A 45-year old woman who had previously known asthma was referred to our clinic for evaluation of a right paratracheal lesion found on her chest roentgenogram. After clinical work-up, we detected a cystic lesion in the middle mediastinum. Surgical excision was performed via thoracotomy. Histopathologic study revealed a thymic cyst. In this case, we report a rare localization of thymic cyst presenting as a middle mediastinal mass. ©Copyright 2011 by Gazi University Medical Faculty.