Thymic cysts are rare lesions of the anterior mediastinum or neck. The majority are asymptomatic, and the remainder are associated mainly with symptoms of dysphagia or dyspnea. Diagnosis is difficult before surgery. Cervical thymic cysts are relatively rare; age at presentation ranges from the neonatal period to adulthood, and the most frequent presenting sign is a lateral neck mass. Mediastinal thymic cysts are more common and account for 1% of all mediastinal masses. They tend to occur in the older age group and are usually detected incidentally on chest X-ray film or computed tomography scans. Dysphagia and dyspnea are the main symptoms. We describe two brothers, aged 5 and 8 years, with mediastinal thymic cysts that presented as low cervical masses and review the embryology, diagnosis and management of thymic cysts.