Background: Specifically young women are at risk for a poor outcome after ST-elevation myocardial infarction (STEMI). We aimed to investigate sex- and age-specific differences in outcome and associate these results with adherence to a guideline-directed optimal medical therapy (OMT). Methods: Administrative insurance data (≈26 million insured) were screened for patients aged 18–60 years with STEMI. Patient demographics, details on in-hospital treatment, adherence to OMT and its effect on mortality were assessed. Adherence to OMT was analyzed using multistate models and an association of those with death was fitted using multivariable Cox regression models with time-dependent co-variables. Results: Overall, 59,401 patients (19.3% women), median age 52 (interquartile range 48, 56) presented with STEMI. Female sex was associated with a poor outcome early after STEMI (90-day mortality: odds ratio 1.22, 95% confidence interval (CI) 1.12–1.32, p < 0.001). Overall survival was reduced in women compared to same-aged men. The ten-year survival rate was 19.7% (18.1–21.2%) versus 19.6% (18.9–20.4%) in men (p < 0.001). Although long-term drug adherence was low, its intake was associated with a better outcome. Specifically younger women showed a markedly lower mortality when on OMT (hazard ratio (HR) 0.22 (95% CI 0.19–0.26) versus HR 0.31 (95% CI 0.28–0.33) in men, p^int < 0.001). Conclusions: Specifically young women were at risk for a poor outcome in the early phase after STEMI. Although long-term adherence to OMT was low, it was generally associated with a lower mortality, specifically in women. Our findings emphasize on early and long-term preventive measures in all patients after STEMI.