When people get low back pain (LBP), it is not always evident when to see a general practitioner (GP) or physiotherapist, or to perform self-care. A direct correct referral is essential for effective treatment to prevent the development of chronic LBP the utmost. In the context of designing a tool that is able to provide a referral advice to a patient, 63 healthcare professionals (GPs and physiotherapists) participated in a vignette study. They had to judge 32 LBP cases on 1. see a general practitioner, 2. see a physiotherapist, and 3. perform self-care. In total, 1288 vignettes were judged. Multinomial regression analysis showed that Weight Loss, Trauma, and Nocturnal Pain are the three most significant predictive variables. A decision tree was generated that showed the same conclusion. This decision tree is the basis to build a tool that provides personalized referral advice to patients with LBP from the very beginning.