AIM:To compare high resolution colonoscopy(Olympus Lucera) with a megapixel high resolution system(Pentax HiLine) as an in-service evaluation.METHODS:Polyp detection rates and measures of performance were collected for 269 colonoscopy procedures.Five colonoscopists conducted the study over a three month period,as part of the United Kingdom bowel cancer screening program.RESULTS:There were no differences in procedure duration(χ2 P = 0.98),caecal intubation rates(χ2 P = 0.67),or depth of sedation(χ2 P = 0.64).Mild discomfort was more common in the Pentax group(χ2 P = 0.036).Adenoma detection rate was significantly higher in the Pentax group(χ2 test for trend P = 0.01).Most of the extra polyps detected were flat or sessile adenomas.CONCLUSION:Megapixel definition colonoscopes improve adenoma detection without compromising other measures of endoscope performance.Increased polyp detection rates may improve future outcomes in bowel cancer screening programs. AIM: To compare high resolution colonoscopy (Olympus Lucera) with a megapixel high resolution system (Pentax HiLine) as an in-service evaluation. METHODS: Polyp detection rates and measures of performance were collected for 269 colonoscopy procedures. Five colonoscopists conducted the study over a three month period, as part of the United Kingdom bowel cancer screening program. RESULTS: There were no differences in procedure duration (χ2 P = 0.98), caecal intubation rates (χ2 P = 0.67), or depth of sedation (χ2 P = 0.64) .Mild discomfort was more common in the Pentax group (χ2 P = 0.036) .Adenoma detection rate was significantly higher in the Pentax group (χ2 test for trend P = 0.01) .Most of the extra polyps detected were flat or sessile adenomas .CONCLUSION: Megapixel definition colonoscopes improve adenoma detection without compromising other measures of endoscope performance. Increased polyp detection rates may improve future outcomes in bowel cancer screening programs.