What happens to my 401(k) if I leave the United States permanently?

Your 401(k) stays yours, leaving the country doesn't forfeit it. You have several options: leave it in the employer plan (if the balance allows), roll it into an IRA so you control the investments, or cash it out. Cashing out before age 59½ usually triggers a 10% early-withdrawal penalty plus income tax, and as a nonresident the plan typically withholds 30% (or a treaty rate) on distributions, so it's the most expensive choice. Many people keep the account invested and let it grow until retirement, then take distributions from abroad. Keep your login, address, and beneficiary info current, and tell the plan you've moved so withholding is handled correctly. Don't cash out in a panic, model the tax hit first.