Performance assessment is challenging to administer and validate, yet remains central to patient safety and quality of care. The aim of this study was to evaluate Consultant Surgeon trainer performance with respect to Workplace Based Assessment (WBA) completion. All WBAs for 60 Core Surgical Trainees (n = 2932) recorded in one academic year were analyzed using the Intercollegiate Surgical Curriculum Progamme. Primary outcome measures were numbers of WBAs performed related to trainer role (Assigned Educational Supervisor vs. Clinical Supervisor vs. No Training Role), gender, surgical subspecialty, hospital status (teaching vs. district general), and trainer RCSEng. TrACE course accreditation. A core surgical training program serving a single UK (Wales) deanery. Sixty consecutively appointed core surgical trainees. Median WBA number performed irrespective of trainer role was 6 (range 0-51), consisting of CBD 2 (0-18), mini-CEX 2 (0-22), DOPS 2 (0-32), and PBA 0 (0-10). Assigned Educational Supervisor trainers were more likely to complete the full range of WBAs compared with Clinical Supervisor and No Training Role assessors; WBA 17 vs. 6 vs. 3; CBD 5 vs. 2 vs. 1; mini-CEX 5 vs. 2 vs. 1; DOPS 4 vs. 2 vs. 1; and PBA 0 vs. 0 vs. 0 (p < 0.001). WBAs completed varied by subspecialty; first quartile performance: ENT, Plastic Surgery, (median 12, interquartile range 13), compared with fourth quartile: OMFS, Urology, T&O, and Cardiothoracic Surgery (median 5, interquartile range 11, p = 0.016). Hospital status, gender, and TrACE accreditation were not associated with WBA performance. Important variations in trainer WBA completion were apparent; training programme directors and trainees alike should be aware of this when agreeing educational contracts.