1. Four cases of parathyroid cysts and one case of cervical thymic cyst were seen in our hospital during 8 years of observation.2. Diagnostic criteria was discussed to rule out the secondary change of cystic formation.3. Comparative studies indicated that both cysts seemed to develop congenitally from the thymopharyngeal duct system. 4. Both cysts were considered to be a rare entity. However, it may be possible to find them more frequently if sections of histopathological specimens are carefully taken from various sites.