In the Request for an Advisory Opinion Submitted by the Sub-Regional Fisheries Commission, the International Tribunal for the Law of the Sea (ITLOS) was called upon to clarify the existence of its advisory jurisdiction as a full Tribunal under the UN Convention on the Law of the Sea (UNCLOS). ITLOS unanimously upheld its advisory jurisdiction, yet its reasoning is not convincing. ITLOS’s interpretation of Article 21 of its Statute appears unpersuasive. The article discusses the interpretation of Article 21 ITLOS Statute pursuant to the rules on interpretation of the Vienna Convention on the Law of Treaties (Arts. 31–33). First, the article addresses the article's textual reading, and criticizes the Tribunal's interpretation of the term ‘matters’. Second, the article considers the interpretation of Article 21 according to the subsequent practice of the parties, argued by some states but not addressed by ITLOS. Third, the travaux préparatoires of the UNCLOS are examined, with a view to understanding whether the drafters intended the Tribunal to have advisory jurisdiction. Fourth, the six authentic texts of UNCLOS are compared in order to highlight potential differences that may help understand the exact meaning of the provision. Fifth, the article discusses the relationship between advisory jurisdiction and state consent. The conclusion is that the basis for ITLOS's advisory jurisdiction under UNCLOS seems weak. Some general considerations conclude the article, together with a possible solution that takes stock of ITLOS's decision.