Article 9 of the Nationality Law of the People’s Republic of China says:

定居外国的中国公民,自愿加入或取得外国国籍的,即自动丧失中国国籍。

Any Chinese national who has settled abroad and who has been naturalized as a foreign national or has acquired foreign nationality of his own free will shall automatically lose Chinese nationality.

Apparently the “automatically” isn’t so automatic. Our son was born in China, but never got his official papers like a hukou or ID card, and got a US passport shortly thereafter. To leave China, he still had to get an exit permit, though, and it turns out that this has become his most important official Chinese ID. We went to the Chinese consulate in Chicago yesterday to get him a visa to China, only to be told by them that they still consider him a Chinese citizen until he renounces his Chinese citizenship. You can only renounce your citizenship at the PSB in China they said, and he would have to travel to China as a Chinese citizen on a travel permit. The good thing is that this permit costs a lot less than the visa for US citizens, but the bad thing is if he doesn’t renounce his citizenship before he’s 18, he might be stuck in some sort of bureaucratic limbo and never be allowed into China again. Also, the only way he can get this travel permit is with his old exit permit… good thing we didn’t throw it away.