ImportanceLarge-scale motorcycle rallies attract thousands of attendees and are associated with increased trauma-related morbidity and mortality.ObjectiveTo examine the association of major US motorcycle rallies with the incidence of organ donation and transplants.Design, Setting, and ParticipantsThis population-based, retrospective cross-sectional study used data from the Scientific Registry of Transplant Recipients for deceased organ donors aged 16 years or older involved in a motor vehicle crash and recipients of organs from these donors from March 2005 to September 2021.ExposureDates of 7 large US motorcycle rallies and regions near these events.Main Outcomes and MeasuresThe main outcomes were incidence of motor vehicle crash–related organ donation and number of patients receiving a solid organ transplant from these donors. An event study design was used to estimate adjusted rates of organ donation during the dates of 7 major US motorcycle rallies compared with the 4 weeks before and after the rallies in rally-affected and rally-unaffected (control) regions. Donor and recipient characteristics and metrics of organ quality were compared between rally and nonrally dates.ResultsThe study included 10 798 organ donors (70.9% male; mean [SD] age, 32.5 [13.7] years) and 35 329 recipients of these organs (64.0% male; 49.3 [15.5] years). During the rally dates, there were 406 organ donors and 1400 transplant recipients. During the 4 weeks before and after the rallies, there were 2332 organ donors and 7714 transplant recipients. Donors and recipients during rally and nonrally dates were similar in demographic and clinical characteristics, measures of organ quality, measures of recipient disease severity, and recipient waiting time. During rallies, there were 21% more organ donors per day (incidence rate ratio [IRR], 1.21; 95% CI, 1.09-1.35; P = .001) and 26% more transplant recipients per day (IRR, 1.26; 95% CI, 1.12-1.42; P < .001) compared with the 4 weeks before and after the rallies in the regions where they were held.Conclusions and RelevanceIn this cross-sectional study, major motorcycle rallies in the US were associated with increased incidence of organ donation and transplants. While safety measures to minimize morbidity and mortality during motorcycle rallies should be prioritized, this study showed the downstream association of these events with organ donation and transplants.