ERISA requires plan fiduciaries to discharge their duties for the "exclusive purpose" of providing participants and beneficiaries with benefits. Courts have similarly compared the exclusive benefit requirement under ERISA to the duty of loyalty under the common law of trusts, i.e., the duty to act with "complete and undivided loyalty to the beneficiaries of the trust, and with an eye single to the interests of the participants and beneficiaries. Even when a plan portfolio profits on an overall basis, the disloyal fiduciary risks liability.

A trustee has a fiduciary duty to inform participants and beneficiaries of their rights. A fiduciary must give complete and accurate information in response to participants' questions, a duty that does not require the fiduciary to disclose its internal deliberations nor interfere with the substantive aspects of the bargaining process. Negligent or intentional misrepresentations concerning eligibility for or the extent of benefits violate the duty of loyalty. A plan administrator must speak truthfully. An employer serving as plan administrator cannot keep its participant-contact personnel in the dark about pertinent facts to evade disclosure to the participants. However, an ERISA fiduciary is not under any obligation to offer precise predictions about future changes to its plan. A truthful statement made in good faith creates no breach of duty if participants misunderstand it.