ObjectivesYoung patients account for about half of ST-segment elevation myocardial infarction (STEMI) patients and display a unique risk profile compared with old patients. Whether these differences are related to disparities in ventricular remodeling remains unknown. This study aimed to evaluate age-related differences in ventricular remodeling after primary percutaneous coronary intervention (PPCI) for STEMI.MethodsIn this observational study, consecutive STEMI patients between October 2019 and March 2021 who underwent serial cardiovascular magnetic resonance at index admission (3 to 7 days) and 3 months after PPCI were enrolled. Adverse remodeling was defined as ≥ 10% enlargement in left ventricular end-diastolic volume index (LVEDVi), while reverse remodeling was defined as a decrease in left ventricular end-systolic volume index (LVESVi) of more than 10%.ResultsA total of 123 patients were included and grouped into young (< 60 years,n= 71) and old (≥ 60 years,n= 52) patients. Despite generally similar baseline structural and infarct characteristics, LVESVi significantly decreased only in old patients during follow-up (p= 0.034). The incidence of adverse remodeling was higher (49.3% vs 30.8%,p= 0.039), while the incidence of reverse remodeling was lower (31.0% vs 53.8%,p= 0.011) in young compared with old patients. Younger age (< 60 years) was associated with a significantly higher risk of adverse remodeling (adjusted OR 3.51, 95% CI 1.41–8.74,p= 0.007) and lower incidence of reverse remodeling (adjusted OR 0.42, 95% CI 0.18–0.97,p= 0.046).ConclusionsIn STEMI patients undergoing PPCI, young patients are at a higher risk of adverse remodeling and less probably develop reverse remodeling than old patients. Equal or more attention should be paid to young patients with STEMI compared with their older counterparts.Key Points•In STEMI patients undergoing PPCI, young patients displayed unfavorable remodeling compared with old patients.•Young patients are at a higher risk of adverse remodeling and less probably develop reverse remodeling than old patients.•Equal or more attention should be paid to young patients compared with their older counterparts.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00330-023-09406-5.