ObjectiveCombat Stress, a UK national charity for veterans with mental health problems, has been funded by the National Health Service (NHS) to provide a national specialist service to deliver treatment for post-traumatic stress disorder (PTSD). This paper reports the efficacy of a PTSD treatment programme for UK veterans at 6 months follow-up.DesignA within subject design.SettingUK veterans with a diagnosis of PTSD who accessed Combat Stress.Participants246 veterans who received treatment between late 2012 and early 2014.InterventionAn intensive 6-week residential treatment programme, consisting of a mixture of individual and group sessions. Participants were offered a minimum of 15 individual trauma-focused cognitive behavioural therapy sessions. In addition, participants were offered 55 group sessions focusing on psychoeducational material and emotional regulation.Main outcome measuresClinicians completed measures of PTSD and functional impairment and participants completed measures of PTSD, depression, anger and functional impairment.ResultsWe observed significant reductions in PTSD scores following treatment on both clinician completed measures (PSS-I: −13.0, 95% CI −14.5 to −11.5) and self-reported measures (Revised Impact of Events Scale (IES-R): −16.5, 95% CI −19.0 to −14.0). Significant improvements in functional impairment were also observed (eg, Health of the Nation Outcome Scales (HONOS): −6.85, 95% CI −7.98 to −5.72). There were no differences in baseline outcomes between those who completed and those who did not complete the programme, or post-treatment outcomes between those we were able to follow-up at 6 months and those lost to follow-up.ConclusionsIn a naturalistic study we observed a significant reduction in PTSD scores and functional impairment following treatment. These improvements were maintained at 6 month follow-up. Our findings suggest it may be helpful to take a closer look at combining individual trauma-focused cognitive behaviour therapy and group sessions when treating veterans with PTSD. This is the first UK study of its kind, but requires further evaluation.