Many people with chronic whiplash associated disorders (WAD) also have symptoms of posttraumatic stress disorder (PTSD), but this is rarely considered in usual predominantly exercise based interventions. We aimed to investigate the effectiveness of combined trauma focused cognitive behavioural therapy (TF-CBT) and exercise compared to supportive therapy (ST) and exercise for people with chronic WAD and PTSD. A randomised controlled multi-centre trial with concealed allocation, assessor blinding, and blinded analysis was conducted. 103 participants with chronic WAD (>3 months and <5 years, grade II) and PTSD were randomised to TF-CBT and exercise (n=53) or ST and exercise (n=50). Both interventions comprised 10 weeks of TF-CBT or ST followed by 6 weeks of exercise. Outcomes were measured at baseline, 10 weeks, 16 weeks, 6 months, and 12 months post-randomisation. Analysis was intention to treat using linear mixed models. There was no difference between the interventions on the primary outcome of neck pain related disability at any time point. At 16 weeks, the treatment effect on the 0-100 Neck Disability Index was 0.59 (95% CI 5.51 to -4.33), at 6 months 1.18 (6.15 to -3.78), and at 12 months 1.85 (6.81 to -3.11). In addition, there was no difference between the interventions for the majority of secondary outcomes at any time. Exceptions were in favour of TF-CBT and exercise, where improvements in PTSD symptoms were found at 16 weeks. From 16 weeks onwards, both groups achieved a clinically important improvement in neck pain related disability. However, both groups remained moderately disabled.