At least you can have peace of mind over this one thing: The fiduciary custodian of your 40l(k) plan is absolutely bound by your written designation of beneficiary for your account.However, because of the potential controversy over this situation, I would like to make a few suggestions. First, once again, file notice of your desire to have the two named beneficiaries split the account 50/50 upon your death. Make two copies. Have both notarized. Make sure the notarized and dated copy is in the 40l(k) plan custodian files -- and give one copy to your boyfriend.Second, you need to do some other planning if you are in a long-term committed relationship. For example, you should each give the other a healthcare power of attorney -- so there is no doubt about who would make decisions in case of an accident or illness. Second, you each need a "living will" -- documenting your wishes about end-of-life care. And third, if you have joint property, such as real estate or artwork or other valuables you have collected, you might want to make a will or revocable living trust, detailing where each of you wants your property to go in the event of death or incapacity. As of now, since you are not married, your mother is the automatic beneficiary of your estate -- and could come swooping in to grab your stuff if you are incapacitated, or when you die.That's why you need an estate planning attorney in your state to make all of this legal. Check with your state bar association for a referral. And remember EACH of you needs the same documents! Don't procrastinate!! That's just tempting fate!And now I am going to step over the line. Once you have all these documents created, and have a sound legal footing for your relationship, why not give it a try to tell your mother who you really are. After all, you obviously love her enough to leave her half your fortune. I'm betting she loves you enough that -- once she gets over the shock -- her love for you will win out. What do you have to lose at this point, by trying? A mother's love is a very powerful force. Don't underestimate that.