Distinct developmental trajectories for neck disability and posttraumatic stress disorder (PTSD) symptoms after whiplash injury have recently been identified. This study aimed to identify baseline predictors of membership to these trajectories and to explore their dual development. In a prospective study, 155 individuals with whiplash were assessed at <1 month, 3, 6, and 12 months postinjury. Outcomes at each time point were assessed according to the Neck Disability Index and the Posttraumatic Stress Diagnostic Scale. Baseline predictor variables were age, gender, initial pain (based on a visual analogue scale [VAS]), pressure pain thresholds (PPT), cold pain thresholds (CPT), and sympathetic vasoconstrictor responses. Group-based trajectory analytical techniques were used to parameterise the optimal trajectories and to identify baseline predictors. A dual trajectory analysis was used to explore probabilities of conditional and joint trajectory group membership. CPT ? 13à(OR = 26.320, 95% CI = 4.981-139.09), initial pain level (VAS) (OR = 4.3, 95% CI = 4.98-139.1), and age (OR = 1.109, 95% CI = 1.043-1.180) predicted a chronic/severe disability trajectory. The same baseline factors also predicted chronic moderate/severe PTSD (CPT ? 13ì OR = 9.7, 95%CI = 2.22-42.44; initial pain level [VAS]: OR = 2.13, 95% CI = 1.43-3.17; age: OR = 1.07, 95% CI = 1.01-1.14). There was good correspondence of trajectory group for both disability and PTSD. These findings support the proposal of links between the development of chronic neck related disability and PTSD after whiplash injury.