Introduction Seeing and treating patients in daily practice forms the basis of general practitioner (GP) training. However, the types of patients seen by GP trainees do not always match trainees’ educational needs. Knowledge about factors that shape the mix of patient types is limited, especially with regard to the role of the professionals who work in the GP practice. Aim We investigated factors affecting the mix of patients seen by GP trainees from the perspective of professionals. Design and setting This qualitative study involved GP trainees, GP supervisors, medical receptionists and nurse practitioners affiliated with a GP Specialty Training Institute in the Netherlands. Methods Twelve focus groups and seven interviews with 73 participants were held. Data collection and analysis were iterative, using thematic analysis with a constant comparison methodology. Results The characteristics of patients’ health problems and the bond between the doctor and patient are important determinants of GP trainees’ patient mix. Because trainees have not yet developed bonds with patients, they are less likely to see patients with complex health problems. However, trainees can deliberately influence their patient mix by paying purposeful attention to bonding with patients and by gaining professional trust through focused engagement with their colleagues. Conclusion Trainees’ patient mix is affected by various factors. Trainees and team members can take steps to ensure that this mix matches trainees’ educational needs, but their success depends on the interaction between trainees’ behaviour, the attitudes of team members and the context. The findings show how the mix of patients seen by trainees can be influenced to become more trainee centred and learning oriented.