Study design:Multifaceted: extensive discussions at workshop and conference presentations, survey of experts and feedback.Objectives:Present the background, purpose and development of the International Spinal Cord Injury (SCI) Data Sets for Non-Traumatic SCI (NTSCI), including a hierarchical classification of aetiology.Setting:International.Methods:Consultation via e-mail, presentations and discussions at ISCoS conferences (2006-2009), and workshop (1 September 2008). The consultation processes aimed to: (1) clarify aspects of the classification structure, (2) determine placement of certain aetiologies and identify important missing causes of NTSCI and (3) resolve coding issues and refine definitions. Every effort was made to consider feedback and suggestions from participants.Results:The International Data Sets for NTSCI includes basic and an extended versions. The extended data set includes a two-axis classification system for the causes of NTSCI. Axis 1 consists of a five-level, two-tier (congenital-genetic and acquired) hierarchy that allows for increasing detail to specify the aetiology. Axis 2 uses the International Statistical Classification of Diseases (ICD) and Related Health Problems for coding the initiating diseases(s) that may have triggered the events that resulted in the axis 1 diagnosis, where appropriate. Additional items cover the timeframe of onset of NTSCI symptoms and presence of iatrogenicity. Complete instructions for data collection, data sheet and training cases are available at the websites of ISCoS (http://www.iscos.org.uk) and ASIA (http://www.asia- spinalinjury.org).Conclusions:The data sets should facilitate comparative research involving NTSCI participants, especially epidemiological studies and prevention projects. Further work is anticipated to refine the data sets, particularly regarding iatrogenicity.