Background: Theoretical testing provides the necessary foundation to perform technical skills. Additionally, testing improves the retention of knowledge. Objectives: The aims of this study were to develop a multiple-choice test in endosonography for pulmonary diseases and to gather validity evidence for this test. Methods: Initially, 78 questions were constructed after informal conversational interviews with 4 international experts in endosonography. The clarity and content validity of the questions were tested using a Delphi-like approach. Construct validity was explored by administering the test to 3 groups with different levels of endosonography experience: 27 medical students, 18 respiratory physicians with limited endosonography experience, and 14 experts in endosonography. Results: Two Delphi iterations reduced the test to 52 questions. After item analysis, the final test consisted of 46 questions with a mean item discrimination of 0.47 and a mean item difficulty of 0.63. The internal consistency reliability was calculated at 0.91. The 3 groups performed significantly differently (ANOVA: p < 0.001), and post hoc tests were significant. The experts performed significantly more consistently than the novices (p = 0.037) and the intermediates (p < 0.001). Conclusions: This study provides a theoretical test in endosonography consisting of multiple-choice questions. Validity evidence was gathered, and the test demonstrated content and construct validity.