Objective:To analyze the patterns and causes of tennis-related injuries using, for the first time, a nationally representative data set.Design:A retrospective cohort analysis was performed using the National Electronic Injury Surveillance System database.Setting:All tennis-related injuries treated in US emergency departments (EDs) from 1990 to 2011 were analyzed.Patients:During the study period, an estimated 492002 (95% confidence interval, 364668-619336) individuals, aged 5 to 94 years, presented to US EDs for tennis-related injuries.Assessment of Risk Factors:Independent variables included patient age and gender, mechanism of injury, and location of injury event.Main Outcome Measures:Outcome variables included injury diagnosis, body region injured, disposition from ED, and involvement of the net.Results:Most injuries were sustained by a nonspecific mechanism during play (37.9%) and occurred at a sport or recreation facility (83.4%). Children aged 5 to 18 years had a higher mean injury rate than adults older than 19 years. The most commonly injured body regions were the lower extremities (42.2%) and upper extremities (26.7%). Sprains or strains (44.1%) were the most common type of injury. The number of tennis-related injuries decreased by 41.4% during the years 1990 to 2011, and the tennis-related injury rates decreased by more than 45% during the study period. Among the 3.4% of patients who were admitted to the hospital, two-thirds (65.6%) involved patients 56 years of age or older.Conclusions:Despite the decrease in tennis-related injuries, the growing popularity of this sport warrants increased efforts to prevent injuries, especially among child and older adult participants.