Fees for 401(k)s are a hot issue right now -- participants are suing, regulators are tinkering with the rules, and Congress is considering a rewrite. It's a complex topic, but suffice it to say: Don't believe it if an adviser says his services cost nothing -- you're paying for it, one way or another. Here's a breakdown of the fees to watch for.

MUTUAL FUND FEES Hidden fees are especially common among fund companies competing in the small-business market. They embed administrative fees in the fund expense, for instance. When insurers wrap funds in annuities, they add features -- including a guaranteed income option and an easy annuity rollover -- but often layer extra fees on top of the usual expenses. And brokers collect commissions, which fund companies recover by selling a share class with higher expense ratios.

UP-FRONT VS. EMBEDDED FEES Retirement-plan consultant Shelton urges clients to avoid embedded costs and arrange up-front fees when possible. Company owners ultimately pay that expense, either as the plan's sponsors or as its leading participants; better to take it as a tax deduction than to have it eat away at investment returns.

ADVISER AND ADMINISTRATOR FEES Investment advisers generally charge fees as a percentage of plan assets; figure a quarter of a percent to 1 percent of assets, depending on the services offered, and more if they're taking on an administrative role. Third-party administrators typically charge a base fee of about $1,000 plus $25 to $35 per participant. Sometimes those fees are partially offset by commissions paid by the fund companies to the plan administrators.