The United States International Trade Commission (ITC) has recently become an important adjudicator of patent infringement disputes, and the administrative law judges (ALJs) on the ITC are widely viewed as experts on patent law. This Article empirically examines the performance of the ITC in patent claim construction cases. The Article also compares the performance of the ITC on claim construction with that of federal district courts of general jurisdiction. This study does not find any evidence that the patent-experienced ALJs of the ITC are more accurate at claim construction than district court judges or that the ALJs learn from the Federal Circuit's review of their decisions. When considered in the context of previous studies, the results of this study hint at three possible explanations for the lack of evidence: (1) trial judges (including the ALJs of the ITC) cannot master claim construction, especially without a technical background; (2) the Federal Circuit's claim construction case law is poorly articulated; or (3) claim construction is inherently indeterminate.