Whiplash-related injuries and manifestations, typically neck pain, following car collisions are known to potentially disable individuals with a high and increasing cost to society. There is limited knowledge regarding the temporomandibular joint (TMJ) sequelae following whiplash trauma. Previous studies are typically based on retrospective data and few follow-ups are prospective and controlled in design. Furthermore, previous follow-ups have not included magnetic resonance (MR) imaging, which is a prerequisite for verification of TMJ status. The aims of this prospective long-term study were (i) to determine frequency of inaccurate recall of TMJ symptoms in patients with a history of whiplash trauma, and (ii) to evaluate incidence, prevalence and progression of TMJ pathology, verified with MR imaging, and TMJ symptoms in patients after whiplash trauma, compared with the natural course in matched volunteers. We studied 60 consecutive patients who had neck symptoms following a rear-end car collision and were seen at a hospital emergency department. Bilateral TMJ MR imaging and clinical examination were performed at inception and at follow-up on average 15 years later. A self-administered questionnaire regarding TMJ symptoms (pain, dysfunction, or both) and a subsequent interview were performed at inception, at the one-year, and 15-year follow-up. Fifty-seven patients (95%) participated in all three examinations (85% for MR imaging examinations). Concurrently, 53 volunteers matched by age and sex followed the same protocol. Fifty volunteers (94%) participated in all three examinations (89% for MR imaging examinations). Ethics approval of the study protocol and informed consent from all participants was obtained. The calculated agreement between each patient’s inceptive and retrospective reports on TMJ symptoms yielded a kappa value of 0.41 (95% CI 0.18-0.64). Sixteen patients (40%) had inaccurate recall one year after whiplash trauma. There was no statistically significant difference in TMJ symptoms reported by the patients to be present before whiplash trauma compared with matched volunteers at inception. Prevalence of TMJ symptoms increased significantly with whiplash trauma and the increase remained stable throughout the 15-year study period, which contrasted to the natural course in volunteers. After one year the difference in prevalence between patients and volunteers was 54% versus 21% (p=0.0003) and after 15 years 49% versus 18% (p=0.0017). There was no statistically significant difference between patients and volunteers in prevalence of TMJ disc displacement either at inception (63% versus 53%) or at 15-year follow-up (63% versus 55%). TMJ disc displacement was significantly more prevalent in symptomatic volunteers compared with asymptomatic volunteers (89% versus 31%, p=0.0002). Incidence or progression of MR imaging verified TMJ pathology did not differ between patients and volunteers. This prospective 15-year follow-up concludes - that future studies on TMJ sequelae following whiplash trauma should be prospective in study design with examinations conducted in close proximity to whiplash trauma. This allows for reliable baseline status and potential bias of inaccurate recall of symptoms is minimized. - that future controlled studies on TMJ pathology in patients should include control groups of not only asymptomatic but also symptomatic volunteers in order to avoid potentially biased conclusions. - that one of three patients exposed to whiplash trauma can be expected to develop TMJ symptoms beyond that which corresponds to the natural course in volunteers. This finding and previously reported impairment of jaw function in patients with symptoms after whiplash trauma points to the need for including TMJs and related muscles in routine medical examinations of patients with symptoms following whiplash trauma. - that adult individuals presenting with no or mild TMJ symptoms seldom show development or aggravation of TMJ pathology and there is no or little indication for TMJ treatment of these adult individuals. This is in contrast to the higher progression of TMJ pathology previously reported for adult patients with TMJ symptoms, which requires treatment.