I rolled over a Roth 401(k) to a Roth IRA and was charged a fee by the outgoing financial institution. This fee was paid from the account balance. Is this fee deductible as an investment expense? If this were for a traditional 401(k), it's pre-tax money, so the deduction wouldn't really make sense, but since it's a Roth 401(k), the money's been taxed.
If the fee is paid directly from the account, then unfortunately no, you can not deduct it. It's probably too late now, but in the future you can ask the financial institution if they will allow you to write them a separate check to cover the fees. If they allow that then you can preserve your tax free account balance, and potentially deduct the fees too. More details here.
Update: as discussed in the comments below, a strict interpretation of the IRS description of deductible investment expenses may not include expenses for a Roth IRA, even if they are paid outside of the account. However, there seems to be conflicting interpretations of this IRS rule, so I would advise speaking to an accountant or the IRS directly for clarification. But even if you determine you cannot deduct the fees, paying for them outside of the Roth is still a good idea because it enables you to maintain a higher balance in your tax advantaged account.