Earlier this year I rolled over my 401(k) to Vanguard and a portion of it was after-tax $$. Vanguard advised me to put the after-tax $$ into a traditional IRA and the pre-tax $$ into a rollover IRA to keep the two separate -- as I plan to withdraw after-tax $$ before I touch the pre-tax $$ when I start to take distributions from my IRA. They also advised me to submit an 8606 form to the IRS for the amount of after-tax $$ I moved to Vanguard with my '07 tax return. Like the OP, I never filed this form during my employment -- in fact, I never heard of it before VG told me about it.