OBJECTIVES: We evaluated a new assessment technique for colonoscopy training. METHODS: We prospectively evaluated colonoscopy skills during training using the Rotterdam Assessment Form for colonoscopy. The questionnaire covers cecal intubation, procedural time, and subjective grading of performance. Individual learning curves are compared with a group reference. RESULTS: Nineteen trainees self-assessed 2,887 colonoscopies. The cecal intubation rate improved from 65% at baseline to 78% and 85% after 100 and 200 colonoscopies, respectively. In our training program the 90% threshold was reached after 280 colonoscopies on average. Cecal intubation time improved from 13:10 minutes at baseline to 9:30 and 8:30 after 100 and 200 colonoscopies, respectively. CONCLUSIONS: This novel self-assessment form allows individual learning curves to be compared with a group reference, provides data on the development of dexterity skills and individual training targets, and stimulates trainees to identify steps for self-improvement.