Background: Case finding was improved to the population-based method at the Isfahan Cancer Registry (ICR) during 2005-2008. However, its effects on the number of registered colorectal cancer (CRC) cases and patients' age are not investigated. Therefore, present study designed to investigate the effect of that improvement on the trend of incidence of CRC, and age of CRC cases in ICR's catchment area., Methods: Data from the ICR were retrieved by years for 2000-2011. Annual age-standardized incidence rates (ASRs), truncated ASRs and 95% confidence intervals (95% CIs) were estimated for both genders. Rates were standardized based on the 2000 world standard population. Trends were analyzed, and significant change-points were identified using Joinpoint Regression software. Age of CRC cases compared between periods before and after the improvement., Results: A total of 2902 CRC cases had been registered by ICR. Estimated ASRs (95% CI) for 2000 and 2011 were 3.47 (3.45, 3.50) and 10.22 (10.19, 1025) per 100,000 persons, respectively. Two significant change-points were identified (i.e., at 2003 and 2006). However, estimated average annual percent change was as 11. There was no significant difference between mean of patients' age before and after the time of improvement ( P = 0.88)., Conclusions: Trends of incidence of CRC had been rising in central Iran for males and females, during 2000-2011. It seems that the estimated slope for this trend had been partially artificial and significantly affected by the improvement of case-finding method. However, the improvement had no effect on the patients' age., Competing Interests: There are no conflicts of interest.