In a series of recent disputes arising under the TBT Agreement, the Appellate Body has interpreted Article 2.1 to provide that discriminatory and trade-distortive regulation could be permissible if based upon a “legitimate regulatory distinction.” In its recent compliance decision in the US-Tuna II dispute, the AB reaffirmed its view that regulatory distinctions embedded in the U.S. dolphin-safe tuna labeling regime were not legitimate because they were not sufficiently calibrated to the risks to dolphins associated with different tuna fishing conditions. This paper analyzes the AB’s application of the notion of risk-based regulation in the US-Tuna II dispute and finds the AB’s reasoning lacking in coherence. Although risk analysis and calibration can in principle play useful roles in TBT cases, the AB needs to provide more explicit and careful guidance to WTO members and to panels to avoid the kind of ad hoc decision-making exhibited throughout the US-Tuna II dispute.