Studies of migrants, along with geographic and temporal variations in incidence, indicate that colorectal cancer is especially sensitive to changes in environmental factors, including, most importantly, diet. The goal of this research was to examine the changes in dietary practices that may be consistent with the changing incidence of colorectal cancer in the Los Angeles Mexican-American population. Cancer incidence and dietary intake data were available for over 35,000 Latinos of Mexican national origin currently participating in the prospective Multiethnic Cohort Study, representing the largest sample of Mexican-origin Latinos of any such study in the United States. The dataset is unique in that changes in cancer rates and in dietary behaviors across three generations could be examined. Most of the change in colorectal cancer rates occurred between the first and second generations, and, correspondingly, nearly all the dietary change also occurred between the first and second generations. Although some food traditions were retained by Mexican Americans, the dietary changes due to acculturation were significant and support an association between colorectal cancer risk and certain dietary components, notably, alcohol as a risk factor and nonstarch polysaccharides and vegetables as protective factors.