BackgroundAssessing primary rehabilitation needs in patients with acquired brain injury is a challenge due to case complexity and the heterogeneity of symptoms after brain injury. The Rehabilitation Complexity Scale-Extended (RCS-E) is an instrument used in assessment of rehabilitation complexity in patients with severe brain injury. The aim of the present study was to translate and test the face validity of the RCS-E as a referral tool for primary rehabilitation. Face validity was tested in a sample of patients with acquired brain injury.MethodsTen clinicians and records from 299 patients with acquired brain injury were used in the translation, cross-cultural adaptation and face validation study of the RCS-E. RCS-E was translated into Danish by a standardized forward-backward translation by experts in the field. Face validity was assessed by a multi-professional team assessing 299 patients. The team was asked their opinion on whether the RCS-E presents a sufficient description of the patients.ResultsThe RCS-E was translated according to international guidelines and tested by health professionals; some adaptations were required due to linguistic problems and differences in the national health system structures.The patients in the study had a mean age of 63.9 years (SD 14.7); 61 % were male.We found an excellent face validity with a mean score of 8.2 (SD 0.34) assessed on a 0–10 scale.ConclusionsThe RCS-E demonstrated to be a valid assessment of primary rehabilitation needs in patients with acquired brain injury. Excellent face validity indicates that the RCS-E is feasible for assessing primary rehabilitation needs and the present study suggests its applicability to the Danish health care system.Electronic supplementary materialThe online version of this article (doi:10.1186/s12883-016-0728-7) contains supplementary material, which is available to authorized users.