Study Design Systematic review. Objectives To systematically review the descriptors used to define running-related musculoskeletal injury and to analyse the implications of different definitions on the results of studies. Background Studies have developed their own definitions of running-related musculoskeletal injuries based on different criteria. This may affect the rates of injury, which can be overestimated or underestimated due to the lack of a standard definition. Methods Searches were conducted on EMBASE, PubMed, CINAHL, SPORTDiscus, LILACS and SCIELO databases, without a limit to date of publication and language. We only included articles that reported a definition of running-related injury. The definitions were classified according to three domains and subcategories: 1) presence of physical complaint (symptom, body system involved, region); 2) interruption of training or competition (primary sports involved, extent of injury, extent of limitation, interruption, period of injury); and 3) need for medical assistance. Spearman rank correlation was performed to verify the correlation between the completeness of definitions and the rates of injury reported in the studies. Results A total of 48 articles were included. Most studies described more than half of the subcategories, but with no standardisation between the terms used within each category, showing that there is no consensus for this definition. The injury rates ranged between 3% and 85%, and tend to increase with less-specific definitions. Conclusion The descriptors commonly used by researchers to define an injury vary between studies and may affect the rates of injuries. The lack of a standardised definition hinders comparison between studies and rates of injuries. J Orthop Sports Phys Ther, Epub 26 Mar 2015. doi:10.2519/jospt.2015.5750.