Objective: To establish the dietary knowledge, attitudes and potential barriers to change of patients attending a colorectal outpatient clinic. Design: Use of a semistructured interview to generate qualitative and quantitative data. Setting: A regional colorectal outpatient clinic within Edinburgh. Method: Patients attending clinic with colorectal symptoms were invited to participate in a semistructured interview using a validated questionnaire. Results: Fifty patients (mean age 62 plus or minus SD 15.1 years; male:female = 22:28) were interviewed. Twenty-three (46 per cent) knew that five portions of fruit and vegetable were recommended daily, but 31 (62 per cent) were unclear what constituted a portion. Only three (6 per cent) and two (4 per cent) could name three foods high in fat and fibre, respectively. Twenty-three (46 per cent) were unable to identify why healthy eating is important, while only four (8 per cent) were aware of an association between diet and cancer. Women had significantly higher nutrition knowledge scores than men (16.3 plus or minus SD7.1 v 12.3 plus or minus SD5.1, p less than 0.05 ). There was a significant relationship between educational attainment and nutritional knowledge (r = 0.534, p less than 0.001). Potential barriers to change included the belief that their diet was already healthy (n = 35, 70 per cent) and lack of time (n = 25, 50 per cent). Conclusion: Patients attending a colorectal clinic lack practical dietary knowledge and the majority are unaware of the link between diet and cancer. Targeted health promotion strategies are needed to raise awareness in this group. (Contains 3 tables.)