Colorectal cancer incidence after adenoma removal has been studied in selected populations of adenoma patients. Our study estimates the trend in colorectal cancer incidence after adenoma removal in actual clinical practice. From PALGA, a nationwide network and registry of histo- and cytopathology in the Netherlands, we extracted data of all patients diagnosed with colorectal adenomas between 1 January 1988 and 1 October 1998. The data were used to calculate population-based colorectal cancer incidence rates after adenoma removal. A total of 78,473 adenoma patients were followed for a mean of 4.5 years after the first adenoma removal. The colorectal cancer incidence ratio compared with the general population matched by age and gender was 38.4 (37.3-39.5) in the first year after adenoma removal and 1.5 (95% confidence interval (CI): 1.4-1.6) after Year 1. The incidence ratio decreased from 2.8 (2.5-3.1) in Year 2 to 0.9 (0.6-1.2) in Years 9-11. This time trend is the opposite of the upward time trend that was expected after adenoma removal. Adenoma patients in the Netherlands are at increased risk for colorectal cancer compared to the general population. The high cancer incidence in Years 1-5 after polypectomy can be explained by a colonoscopic sensitivity for cancer of approximately 90%.