OBJECTIVE: To assess whether public understandings of inherited predisposition to colorectal cancer may undermine preparedness to respond to preventive messages. METHODS: Structured in-depth interviews with 31 women and men, aged 50 years and over. RESULTS: Most participants viewed genetic factors as prompts for taking preventive measures rather than as reasons for fatalism and inaction. They were optimistic about the potential benefits of new developments in cancer prevention and treatment. CONCLUSIONS: There was little evidence of perceived genetic determinism in relation to colorectal cancer, but there were some significant misunderstandings about causes, prevention and treatment. These findings have important implications for public health communications about the contribution of genetics to cancer causation.