Comparing results across studies in traumatic brain injury (TBI) has been difficult because of the variability in data coding, definitions, and collection procedures. The global aim of the Working Group on Demographics and Clinical Assessment was to develop recommendations on the coding of clinical and demographic variables for TBI studies applicable across the broad spectrum of TBI, and to classify these as core, supplemental, or emerging. The process was consensus driven, with input from experts over a broad range of disciplines. Special consideration was given to military and pediatric TBI. Categorizing clinical elements as core versus supplemental proved difficult, given the great variation in types of studies and their interests. The data elements are contained in modules, which are grouped together in categories. Three levels of detail for coding data elements were developed: basic, intermediate, and advanced, with the greatest level of detail in the advanced version. In every case, the more detailed coding can be collapsed into the basic version. Templates were produced to summarize coding formats, motivation of choices, and recommendations for procedures. Work is ongoing to include more international participation and to provide an electronic data entry format with pull-down menus and automated data checks. This proposed standardization will facilitate comparison of research findings across studies and encourage high-quality meta-analysis of individual patient data.