OBJECTIVE To evaluate the quality of the evidence on the incidence of sudden cardiac arrest (SCA) and sudden cardiac death (SCD) in athletes and military members and estimate the annual incidence of SCA and SCD. METHODS We searched MEDLINE, Embase, Cochrane CENTRAL, Web of Science, BIOSIS, Scopus, SPORTDiscus, PEDro, and ClinicalTrials.gov from inception to dates between February 21 and July 29, 2019. METHODS Studies in which the incidence of SCA, SCD, or both in athletes or military members aged <40 years was reported were eligible for inclusion. We identified 40 studies for inclusion. METHODS Risk of bias (ROB) was assessed using a validated, customized tool for prevalence studies. Twelve had a low ROB, while the remaining 28 had a moderate or high ROB. Data were extracted for narrative review and meta-analysis. RESULTS Random-effects meta-analysis was performed in studies judged to have a low ROB in 2 categories: (1) 5 studies of regional- or national-level data, including athletes at all levels and both sexes, demonstrated 130 SCD events with a total of 11 272 560 athlete-years, showing a cumulative incidence rate of 0.98 (95% CI = 0.62, 1.53) per 100 000 athlete-years and high heterogeneity (I2 = 78%) and (2) 3 studies of competitive athletes aged 14 to 25 years were combined for a total of 183 events and 17 798 758 athlete-years, showing an incidence rate of 1.91 (95% CI = 0.71, 5.14) per 100 000 athlete-years and high heterogeneity (I2 = 97%). The remaining low-ROB studies involved military members and were not synthesized. CONCLUSIONS The worldwide incidence of SCD is rare. Low-ROB studies indicated the incidence was <2 per 100 000 athlete-years. Overall, the quality of the available evidence was low, but high-quality individual studies inform the question of incidence levels. CRD42019125560.