Background: Changes in dietary practices are known to be associated with changes in the health and disease pattern of a population. This study aimed to qualitatively explore the perception of colorectal cancer patients regarding causes of colorectal cancer and the influence of diet. Materials and Methods: Twelve respondents from three major ethnicities in Malaysia were selected from the quantitative study on dietary pattern and colorectal cancer carried out earlier in this study. In-depth interviews (IDI), conducted from April until June 2012, were mainly in the Malay language with additional use of English and continued until the saturation point was reached. All interviews were autorecorded so that verbatim transcriptions could be created. Results: Causes of colorectal cancer were categorized into internal and external factors. The majority of respondents agreed that there is an association between Western foods and colorectal cancer. Malaysian traditional diet was not related to colorectal cancer as less preservative agents were used. Malaysian diet preparation consisting of taste of cooking (spicy, salty and sour foods) plus type of cooking (fry, grilled and smoked) were considered causes of colorectal cancer. All respondents changed their dietary pattern to healthy food after being diagnosed with colorectal cancer. Advice from doctors regarding suitable food for colorectal cancer was useful in this regard. Conclusions: Eating outside, use of food flavoring ingredients and preservative agents were considered to be the main factors causing colorectal cancer. All respondents admitted that they changed to a healthy diet after being diagnosed with colorectal cancer.