Thymic cysts are usually diagnosed accidentally during radiological evaluation of the chest for unrelated conditions. Symptoms appear late when the mass compresses on adjoining tissues. We report an unusual case of asymptomatic mediastinal thymic cyst which was seen in the neck whenever the patient was asked to perform Valsalva maneuver. This case is being reported for the unusual clinical presentation of a rare disease. The role of imaging in the diagnosis and common differential diagnoses are also discussed.