Background: To reduce complications and increase success, thoracic ultrasound is recommended to guide all chest drainage procedures. Despite this, no tools currently exist to assess proceduralist training or competence. This study aims to validate an instrument to assess physician skill at performing thoracic ultrasound, including effusion markup, and examine its validity. Methods: We developed an 11-domain, 100-point assessment sheet in line with British Thoracic Society guidelines: the Ultrasound-Guided Thoracentesis Skills and Tasks Assessment Test (UGSTAT). The test was used to assess 22 participants (eight novices, seven intermediates, seven advanced) on two occasions while performing thoracic ultrasound on a pleural effusion phantom. Each test was scored by two blinded expert examiners. Validity was examined by assessing the ability of the test to stratify participants according to expected skill level (analysis of variance) and demonstrating test-retest and intertester reproducibility by comparison of repeated scores (mean difference [95% CI] and paired t test) and the intraclass correlation coefficient. Results: Mean scores for the novice, intermediate, and advanced groups were 49.3, 73.0, and 91.5 respectively, which were all significantly different (P < .0001). There were no significant differences between repeated scores. Conclusions: Procedural training on mannequins prior to unsupervised performance on patients is rapidly becoming the standard in medical education. This study has validated the UGSTAT, which can now be used to determine the adequacy of thoracic ultrasound training prior to clinical practice. It is likely that its role could be extended to live patients, providing a way to document ongoing procedural competence.