BACKGROUND: Contemporary trends in traditional and nontraditional risk factors (RFs) among young adults with acute myocardial infarction (AMI) are not well understood. OBJECTIVES: This study sought to determine differences and trends in the prevalence of traditional and nontraditional RFs among young and older adults hospitalized with incident AMI. METHODS: Incident AMI hospitalizations were analyzed from 2011 to 2021 from the National Inpatient Sample and stratified by age (young adults 18-54 years of age and older adults >54 years of age). Overall RF prevalence and trends in traditional (eg, hypertension) and nontraditional (eg, psychosocial factors) RFs were assessed. Subgroup analysis by sex and race/ethnicity was performed. RESULTS: Among 4,431,901 incident AMI hospitalizations, 974,521 (22%) were young adults. Hypertension (64.8%) and tobacco use (57.8%) were the most prevalent RFs in young adults overall. Among 5 traditional RFs, tobacco smoking and obesity were significantly higher in young adults compared to older adults. Among 12 nontraditional RFs, lowest income quartile, family history of ischemic heart disease, and psychiatric disorders were significantly higher in young adults. Within young adults, women and non-Whites had a higher prevalence of both traditional and nontraditional RFs. Across the study period, the prevalence of most traditional and nontraditional RFs in young adults increased significantly (P_trend < 0.050 for all). CONCLUSIONS: Young adults with AMI have a different and increasing burden of both traditional and nontraditional RFs compared to older adults. These findings could help guide strategies for primary prevention of AMI.