Upon leaving a job, the funds in your 401(k) remain yours. You have several options after you quit, including leaving the funds in the old employer's 401(k) or rolling them over into a new employer's plan. You can also roll the previous 401(k) into an IRA or take a distribution in the form of a withdrawal. Individuals under age 55 are subject to a 10% withdrawal penalty, though, and there are likely other tax implications to consider if you withdraw the funds.