Objectives: To identify factors predictive of patient load at major commercial concert first-aid stations, and to characterize the spectrum of presenting injuries and illnesses at such events. Methods: This study was a retrospective case series of patients presenting to on-site first-aid stations at five major concert venues in southern California over a five-year period. The authors compared the number of patients per ten thousand attendees (PPTT) with four potential predictors (music type, overall attendance, temperature, and indoor vs outdoor location) using univariate techniques and negative binomial regression. The spectrum of chief complaints observed is described. Results: There were 1,492 total patients out of 4,638,099 total attendees at 405 separate concerts. The median patient load per concert was 2.1 PPTT, ranging from 0 PPTT at 53 concerts to 71 PPTT at a punk rock festival that turned into a riot. Patient load varied significantly by music category (p = 0.0001) but not with overall attendance, temperature, or indoor vs outdoor location. Median PPTT by music category ranged from 1.3 PPTT for rhythm and blues to 12.6 PPTT for gospel/Christian, with negative binomial regression indicating that rock concerts had 2.5 times (95% CI = 2.0 to 3.0) the overall patient load of non-rock concerts. Music type, however, was able to account for only 4% of the variability observed in the regression model. Trauma-related complaints predominated overall, with similar rates at rock and non-rock concerts. Four cardiac arrests occurred at classical concerts. Conclusion: Rock concert first-aid stations evaluated 2.5 times the patient load of non-rock concerts overall, although there was substantial concert-to-concert variability. Trauma-related complaints predominate at both rock and non-rock events. These data may assist individuals and organizations planning support for such events.