Cross-sectional studies confirm, as expected, a positive association between jaw injury and painful temporomandibular disorders (TMDs), but prospective evaluations are lacking. We prospectively assessed incident jaw injury, injury type, and development of TMD in adults ages 18-44 years.Data were collected from 3,258 individuals from communities surrounding four U.S. academic institutes between 2006 and 2008. At enrollment, participants reported no TMD history and no facial injuries in the previous 6 months. Quarterly follow-up questionnaires assessed incident jaw injury, which was classified as intrinsic (attributed to yawning or prolonged mouth opening) or extrinsic (attributed to other causes). Examiners classified incident TMD during a median follow-up period of 2.8 years (range 0.2-5.2 years). Cox regression models used jaw injury as a time-dependent covariate to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association with incident TMD.Among 1,729 participants with complete data, 175 developed TMD. Eighty percent of injuries were intrinsic. TMD annual incidence was nearly twice as high in those experiencing jaw injury (5.37%) compared to those who did not (3.44%). In the Cox model that accounted for timing of injury, the corresponding HR was 3.94 (95%CI=2.82-5.50) after adjusting for study site, age, race, and gender. Hazard ratios did not differ (p=0.91) for extrinsic injuries (HR=4.03, 95%CI=2.00-8.12) and intrinsic injuries (HR=3.85, 95%CI=2.70-5.49).Jaw injury was strongly associated with incident TMD. If surveillance and intervention following jaw injury is to be effective in preventing TMD, they should focus on both intrinsic and extrinsic injuries.