Background: Coronary artery disease (CAD) in adults aged <= 40 years is increasing, yet long-term outcomes after percutaneous coronary intervention (PCI) in the drug-eluting stent (DES) era remain unclear. We aimed to identify procedural patterns and prognostic factors in this very young cohort. Methods: This single-centre retrospective cohort study included 312 consecutive patients aged <= 40 years who underwent successful PCI for de novo lesions (>= 70% stenosis) between 2014 and 2024. Baseline characteristics, quantitative coronary angiography, and procedural data were collected. The primary endpoint was major adverse cardiovascular and cerebrovascular events (MACCE). Cox regression identified independent predictors. Results: Patients were 82% men (mean age 36.8 +/- 4.9 years) with a median SYNTAX score of 16. Procedural success was 98.4% with 93.9% DES implantation and 85.9% radial access. Over 1,620 patient-years (median 5.2 years), MACCE occurred at 27.8 per 1,000 patient-years (5-year cumulative 14.2%). Cardiac mortality was 3.7 per 1,000 patient-years. Diabetes [adjusted hazard ratios (HR) 1.78, 95% confidence interval (CI) 1.06-2.99], SYNTAX score >= 23 (HR 2.01, 1.19-3.40), and dual antiplatelet therapy <12 months (HR 1.62, 1.00-2.64) independently predicted MACCE. Conclusions: Young adults undergoing PCI exhibit complex anatomy but low cardiac mortality. Diabetes, angiographic complexity, and abbreviated antiplatelet therapy are key drive of adverse events, warranting intensive prevention and optimised antiplatelet strategies.