Background: Colonoscopy is difficult to learn. Virtual reality simulation training is helpful, but how and when novices should progress to patient-based training has yet to be established. To date, there is no assessment tool for credentialing novice endoscopists prior to clinical practice. The aim of this study was to develop such an assessment tool based on metrics provided by the simulator. The metrics used for the assessment tool should be able to discriminate between novices, intermediates, and experts and include essential checklist items for patient safety. Methods: The validation process was conducted based on the Standards for Educational and Psychological Testing. An expert panel decided upon three essential checklist items for patient safety based on Lawshe’s method: perforation, hazardous tension to the bowel wall, and cecal intubation. A power calculation was performed. In this study, the Simbionix GI Mentor II simulator was used. Metrics with discriminatory ability were identified with variance analysis and combined to form an aggregate score. Based on this score and the essential items, pass/fail standards were set and reliability was tested. Results: Twenty-four participants (eight novices, eight intermediates, and eight expert endoscopists) performed two simulated colonoscopies. Four metrics with discriminatory ability were identified. The aggregate score ranged from 4.2 to 51.2 points. Novices had a mean score of 10.00 (SD 5.13), intermediates 24.63 (SD 7.91), and experts 30.72 (SD 11.98). The difference in score between novices and the other two groups was statistically significant (p<0.01). Although expert endoscopists had a higher score, the difference was not statistically significant (p=0.40). Reliability was good (Cronbach’s alpha=0.86). A pass/fail score was defined at 17.1 points with correct completion of three essential checklist items, resulting in three experts and three intermediates failing and one novice passing the assessment. Conclusion: We established a valid and reliable assessment tool with a pass/fail standard on the simulator. We suggest using the assessment after simulation-based training before commencing work-based learning.