Modifiable cardiovascular risk factors (RFs) play a key role in the development of coronary artery disease. We evaluated 20-year trends in RF prevalence among young adults hospitalised with acute coronary syndromes (ACS) in Switzerland. Data were analysed from the Acute Myocardial Infarction in Switzerland (AMIS) Plus registry from 2000 to 2019. Young patients were defined as those aged <50 years. Among 58'028 ACS admissions, 7'073 (14.1%) were young (median 45.6 years, IQR 42.0-48.0), of which 91.6% had at least one modifiable RF, and 59.0% had at least two RFs. Smoking was the most prevalent RF (71.4%), followed by dyslipidaemia (57.3%), hypertension (35.9%), obesity (21.7%) and diabetes (10.1%). Compared with older patients, young patients were more likely to be obese (21.7% vs 17.4%, p < 0.001) and active smokers (71.4% vs 33.9%, p < 0.001). Among young patients, between 2000 and 2019 there was a significant increase in the prevalence of hypertension from 29.0% to 51.3% and obesity from 21.2% to 27.1% (both ptrend < 0.001), but a significant decrease in active smoking from 72.5% to 62.5% (ptrend = 0.02). There were no significant changes in the prevalence of diabetes (ptrend = 0.32) or dyslipidaemia (ptrend = 0.067). Young ACS patients in Switzerland exhibit a high prevalence of RFs, and are more likely than older patients to be obese and smokers. Between 2000 and 2019, RF prevalence either increased or remained stable, except for smoking which decreased but still affected ∼2/3 of young patients in 2019. Public health initiatives targeting RFs in young adults in Switzerland are warranted.