Background: The objectives of the current study were to investigate (1) the longitudinal, reciprocal associations between pain and post-traumatic stress symptoms as proposed by the mutual maintenance model, and (2) to assess the predictive value of the three clusters of post-traumatic stress, where the model revealed that post-traumatic stress symptoms maintained pain in a consecutive cohort of whiplash-injured. Methods: Participants (n = 253; 66.4% women) were people with WAD grades I–III following motor vehicle crashes in Australia. Pain and post-traumatic stress symptoms were assessed by questionnaires over the course of a year (at baseline (<4 weeks), 3, 6 and 12 months post-injury). The objectives were tested using auto-regressive cross-lagged modelling and two additional structural equation models. Results: The analyses revealed that post-traumatic stress symptoms at baseline predicted an increase in pain between baseline and 3 months and that post-traumatic stress symptoms at 6 months predicted an increase in pain between 6 and 12 months, beyond the stability of pain over time. Furthermore, hyperarousal at baseline significantly predicted pain at 3 months and hyperarousal at 6 months significantly predicted pain at 12 months with 16 and 23% explained variance, respectively. [Correction added on 2 March 2018 after first online publication: the explained variance for hyperarousal symptoms at 6 months was previously given incorrectly and has been corrected to 23% in this version.]. Conclusions: The results point to a temporal main effect of post-traumatic stress symptoms on pain over and above the stability of pain itself within the first 3 months post-injury and again in the chronic phase from 6 to 12 months with hyperarousal symptoms driving these effects. From 3 to 6 months, there was a slip in the maintenance patterns with no cross-lagged effects. Significance: Investigating mutual maintenance of pain and PTSS in whiplash, the present study found evidence suggesting a maintaining effect of PTSS on pain within the first 3 months post-injury and from 6 to 12 months driven by hyperarousal, highlighting the importance of addressing PTSS.