According to this article in Schengen News, Greece is working to facilitate a process of recognizing the citizenship of Greek-born adoptees.

There are approximately 3,000 to 5,000 Greek-born adoptees (with the majority living in the USA) some of whom have made the request that they be re-registered as Greek citizens.

Secretary General of the Ministry of the Interior, Nasos Balerbas has stressed “anyone born to a Greek citizen, even if they are adopted, and their parents ask to renounce Greek citizenship, has the right to take it back whenever they want.”