If you have worked in the United States for any length of time (either as a US citizen or a foreign national) it is likely that you have paid into a US pension account such as an IRA (Individual Retirement Account) or a 401k (an occupational pension plan). The question then arises as to what should be done with such an account once you give up US residency.
There are three alternatives: You can transfer it to another pension account, you can distribute the money, or you can leave it in the current account.
In an ideal world you would have complete cross-border portability for your US pension account such that you could transfer the funds without tax consequences to an equivalent account in your new country of residency. Unfortunately US tax regulations typically do not allow such transfers. While you can sometimes transfer from one type of US plan to another without tax consequences (such as from a 401k to an IRA), it is usually not possible to transfer from a US plan to a non-US plan; with the possible exception of some specially structured corporate pension plans. A transfer from a US pension plan to a non-US plan would typically be deemed a distribution for US tax purposes.