Rationale, aims and objectives: QCancer is a cancer risk assessment tool that has been advocated for use in primary care to improve early detection and diagnosis of cancer, but little is known about the views of service users and practitioners on barriers and facilitators to implementing the tool in practice. We aimed to explore the perspectives of service users (adults without a current cancer) and primary care practitioners (GPs and practice nurses) about barriers and facilitators to using QCancer in primary care consultations. Methods: We used a qualitative design, conducting individual interviews and focus groups with a purposive sample of service users and practitioners. Interviews were recorded and transcribed verbatim. Data were analysed using the Framework approach facilitated by NVivo version 10. Results: We interviewed 36 participants (19 service users, 17 practitioners). Barriers to using the tool included: the need for additional consultation time; unnecessary worry generated for some patients; potential for over-referral; practitioner scepticism; potential conflict with existing guidelines; certain symptoms requiring referral at any risk; requirement for training on use of the tool; evidence of effectiveness; and the need to integrate the tool in general practice systems. Participants identified facilitators to use of the tool: supporting decision making; modifying health behaviours; improving speed of referral; and personalising care. Conclusion: The barriers and facilitators identified should be considered when seeking to implement QCancer in primary care. In particular, evidence is needed that the use of this tool improves diagnosis rates without an unacceptable increase in harm from unnecessary investigation.