Objective: To assess 30-day readmission rates and mortality at readmission in nonagenarians following primary percutaneous coronary intervention (pPCI) for ST elevation myocardial infarction (STEMI). Background: There is limited contemporary data exploring the 30-day readmission rates and mortality in nonagenarians (age greater than 90 years) with STEMI following pPCI when compared to no pPCI. Methods: We utilized the National Readmissions Database (NRD) from 2010 to 2018 to identify nonagenarians hospitalized with STEMI. We divided the total cohort into two groups based on pPCI status. We analyzed 30-day readmission rates, mortality at the time of readmission, and causes of readmissions in both study cohorts. Results: Between 2010-2018, an estimated 37,363 STEMI hospitalizations were identified in nonagenarians, of which 12,062 (32.3%) included pPCI and 25,301 (67.7%) had no pPCI. Compared to pPCI cohort, no pPCI had more women (69.8% vs 36.7%), higher elixhauser comorbidity index (13% vs 8%), palliative care consultation (12.6% vs 3.4%), and nursing home placement (48% vs 33.3%) (all p<0.01). Overall, 30-day readmission rates were higher in pPCI cohort compared with no pPCI (22.1% vs 16.2%; p<0.01). However, the in-hospital mortality rates at 30-day readmission were significantly lower in pPCI cohort compared with no pPCI (7.0% vs 14.3%; p<0.01). Heart failure is the most common cause of 30-day readmissions in both cohorts, followed by acute myocardial infarction (MI) and gastrointestinal hemorrhage. Recurrent MI rates were significantly lower in pPCI cohort compared with no pPCI (12.3% vs 18.4%; p<0.01). Conclusion: In nonagenarians with STEMI, pPCI during index hospitalization is associated with slightly higher 30-day readmissions but significantly lower mortality at the time of readmission. Given the remarkable mortality benefit with pPCI, further research is necessary to risk stratify and optimize readmission rates following STEMI in nonagenarians.