Introduction/Purpose The relative age effect (RAE) has been described as the consequence of differences in ages between individuals within the same age group. In youth sports, relatively older children may have a physical and developmental advantage over younger children. The purpose of this study was to determine the relationship between relative age and sports injury in a cohort of pediatric athletes. Methods A probability sample (n = 1997) of children between 5 and 17 yr of age with sports injuries were extracted from a regional hospital database. Relative age was defined as a child's birth month relative to the month that his/her activity uses as an arbitrary age cutoff. The main outcome measure was an activity-specific birth month ratio, which was developed and compared with birth month data for the state. Linear regression models were used to determine overrepresentation and underrepresentation of sports injuries for prepubescent (5-13 yr) and pubescent (14-17 yr) groups separately. Results Among prepubescent patients, the linear regression model indicated a significant RAE on sports injury (R-2 = 0.037), where those born in or right after the cutoff month for their sports were underrepresented in the study cohort relative to their representation in the general population. For the pubescent group, the RAE was reversed, where those born closest, but before the age cutoff date for their sports were the least represented relative to the general population (R-2 = 0.096). Conclusions These results demonstrate an RAE on youth sports injury risk in a cohort of pediatric athletes with sports-related injuries. These findings may be used to inform safe practices within sports participation among youth athletes.