Introduction: National-level data of cancer patients’ readmissions after a ST-segment elevation myocardial infarction (STEMI) are lacking. Objectives: The primary aim of this study was to describe rates and causes of 30-day readmissions in this population. Methods: Among patients who were admitted with STEMI in the United States National Readmission Database (NRD) from October 2015-December 2017, we identified patients with the diagnosis of active breast, colorectal, lung or prostate cancer. The primary endpoint was 30-day unplanned readmission rate. Secondary endpoints included in-hospital outcomes during the index admission and causes of readmissions. A propensity score model was used to compare the outcomes of cancer and no cancer patients. Results: A total of 385,522 patients were included in the current analysis (Cancer= 5,956, No Cancer=379,566). After propensity score matching, 23,880 patients were compared (Cancer=5,949, No Cancer=17,931). Cancer patients had higher 30-day readmission (19% vs 14%, p<0.01). The most common causes for readmission among cancer patients were cardiac (31%), followed by infectious (21%), hematological and oncological (17%), respiratory (4%), stroke (4%) and renal (3%). During the first readmission, cancer patients had higher in-hospital mortality (15% vs 7%; p<0.01) and bleeding complications (31% vs 21%; p<0.01). In multivariate logistic regression, cancer status (OR 1.5, 95% CI 1.2-1.6, p<0.01) was an independent predictor for 30-day readmission. Conclusions: About one in five cancer patients presenting with STEMI will be readmitted within 30 days. Cancer patients’ 30-day readmissions are still predominantly cardiac-related but with a higher proportion of admissions for infectious, cancer-related and bleeding and than those without cancer.