OBJECTIVE: Our aim was to investigate why participants opted out of colonoscopy following a positive screening result for colorectal cancer. DESIGN: Semi-structured, qualitative, single interviews. We audio-recorded and transcribed all interviews verbatim and used Strauss and Corbin's concept of open, axial, and selective coding to identify the main categories shared across all interviews. These formed the basis of our findings. SETTING: A Danish national colorectal cancer screening programme. SUBJECTS: Single interviews with 13 participants who declined to have a colonoscopy. MAIN OUTCOME MEASURES: Reasons to decline colonoscopy after positive screening test. RESULTS: Participants gave 42 different reasons for deciding not to have a colonoscopy and we coded them into nine main categories; Practical barriers, Discomfort of the examination, Personal integrity, Multimorbidity, Feeling healthy, Not having the energy, Belief that cancer is not present, Risk of complications, and Distrust in the accuracy of the iFOBT. CONCLUSIONS: Our findings suggest that some practical barriers could be quite easily addressed, by offering the participants alternative management and procdures. IMPLICATIONS: Further research is needed to examine how widely our findings are represented in the general population, and how general practitioners should consult with patients who have opted out of colonoscopy, despite a positive screening result. Key points Some screening participants are reluctant to proceed with further diagnostic tests for colorectal cancer following a positive screening result. • Interviews with people, who had refused a follow-up colonoscopy, discovered nine categories (42 reasons) of reasons for refusal. • Reluctance can be addressed by offering support with pre-procedure preparations and alternatives to colonoscopy. • General practitioners face ethical dilemmas and challenges, when patients at risk of colorectal cancer decline to proceed with screening.