Background: The life styles of Thai people are changing with westernization and this would be expected to havean impact on the prevalence of cancer and other non-communicable diseases. For planning control programmes it isnecessary to monitor change over time and the present study was conducted to provide information on stomach andcolorectal cancer incidence rates in Khon Kaen Cancer Registry (KKCR), established in 1984 at the Faculty ofMedicine, Srinagarind Hospital, Khon Kaen University. Objective: To assess trends in urban and rural areas ofKhon Kaen province during 1985 - 2004. Methods: Data for stomach and colorectal cancer with an ICD-O diagnosis(coding C16 , C18 – C20) from the population-based cases of the KKCR, registered between 1985 and 2004, wereretrieved and incidence trends were calculated using the Generalized Linear Model method (GLM), which generatesincidence-rate-based logarithms. Results: The study population comprised 2,530 cases, 721 of stomach (males 449,females 272) and 1809 of colorectal (males 976, females 833) cancer. Most cases were aged 35-75 years. Accordingto the histopathological diagnosis, the most common was adenocarcinoma with over 90 percent. The overall agestandardizedincidence rates (ASR) for stomach cancer were 4.5 and 1.4 per 100 000 in males and females, respectively,during 1985-1989, 3.7 and 2.0 during 1990-1994, 3.0 and 2.2 during 1995-1999 and 3.6 and 1.8 during 2000-2004 .The respective figures for colorectal cancer were 3.3 and 2.6, 4.6 and 3.1, 5.4 and 3.5 and finally 5.8 and 5.3. In bothurban and rural areas males were affected more frequently than females, although a shift was evident towardsdecrease in the se ratio was evident for colorectal cancers over time. Discussion: The results of this study showedslight increase in the incidence of colorectal cancer in Khon Kaen province, while rates for stomach cancer remainedquite stable. The findings indicate a need for continuing research in stomach and colorectal cancer epidemiology,with subdivision into particular sites within these two sections of the gut.