The American Association of Endocrine Surgeons drafted Entrustable Professional Activities for Comprehensive Endocrine Surgery to assess trainees in core topics. Fourteen Entrustable Professional Activities were defined. There were 10 "core" Entrustable Professional Activities, with 6 having 3 phases (pre-, intra-, and postoperative) and 4 having a single phase. There were also 4 elective Entrustable Professional Activities, all of which had 3 phases. Beginning in July 2022, 10 institutions collected 3-item microassessments of trainee performance in Entrustable Professional Activities using a web-based platform. Entrustment was measured on a 5-point scale. A total of 698microassessments were submitted between July 2022 and September 2023, with a wide range between programs (3-449, median: 24). Four-hundred ninety-twomicroassessments were completed for endocrine surgery fellows, 6 for chief residents, 6 for postgraduate year 4 students, 166 for postgraduate year 3 students, and 28 for postgraduate year 2 students. Entrustment scores for fellows improved in the second half of the academic year, with 38.2% of microassessments with highest (4/5) entrustment scores in the first 6months of the academic year and 80.1% with highest scores in the second half of the year (P < .001). Intraoperative entrustment scores were lowest in the adrenal category, with only 13 of 117 (11.1%) of microassessments with highest entrustment compared with 85 with 230 (37.0%) in the thyroid category, and 65 of 165 (39.4%) in the parathyroid category (P < .001). Trainees were more likely to achieve highest entrustment in the first 6months for preoperative (36/70, 28.5%) and postoperative (15/28, 53.5%) phases of care, compared with the intraoperative phase of care (79/334, 23.6%) (P < .001). Entrustment scores improved in the second half of the academic year, and trainees were likely to achieve entrustment earlier in nonoperative phases of care.