Objective: To investigate patient preferences and the determinants of participation willingness in orthopaedic diagnostic or invasive surgical randomized controlled trials. Methods: This observational study included one hundred patients visiting an orthopaedic clinic. The patients answered if they were willing to participate in a hypothetical invasive and diagnostic trial among patients with a distal radius fracture. Results: We found no difference in participation willingness in either the invasive surgical (66/100) or the diagnostic trial (68/100, p = 0.76). Willingness to participate was not associated with age, gender, country of origin, level of education, marital status, or distance of home from the hospital with the confidence interval for all odds ratios including the value 1. Patients who expressed willingness to participate do so because they wanted to contribute to science; patients who declined to participate wanted to speak with a doctor and to be better informed. Conclusion: This study showed a high rate of willingness to participate in orthopaedic surgical invasive trials and in diagnostic trials. Nevertheless, to ensure participation, it is recommended to put emphasis on the contribution to science and to give adequate information about the trial including the opportunity to talk to a doctor.