Abstract Background Erectile dysfunction (ED) has been proposed as an early indicator for future coronary and peripheral vascular disease. Aim We aimed to investigate the longitudinal change in proportion and predictors for ED with changes in erectile function domain (EFD) of the International Index of Erectile Function-15 (IIEF-15) in patients with ST-segment elevation myocardial infarction (STEMI) who underwent primary percutaneous coronary intervention (PPCI). Methods Between December 2018 and June 2019, 286 male patients aged between 40 and 70 years who were treated with PPCI for STEMI were included. The patients were asked to complete the IIEF-EFD form 3 days after the procedure for the evaluation of baseline erectile functions. During follow-up 3 months after the index procedure, the patients were asked to refill the IIEF-EFD form. Both baseline and third-month IIEF-EFD scores were calculated, and the patients were classified into ED severity groups as per the IIEF-EFD scores. A linear mixed model was used to identify predictors of ED at 3 months. Outcomes This study identifies the prevalence and predictors of ED with STEMI who underwent PPCI. Results The median age was 54 (range 48–61) years. The median IIEF-EFD scores at 3 days and 3 months were 25.5 (range 20.0–27.0) and 22.00 (range 18.25–25.00), respectively. Half of the patients were found to have ED with varying severity as per baseline IIEF-EFD scores. This rate increased to 79% at the 3-month follow-up visit. The IIEF-EFD scores of the patients decreased over time (P < .001). Advanced age (β = −0.603, se = 0.192, P = .002), presence of three-vessel coronary artery disease (β = −3.828, se = 0.783, P < .001), and diabetes (β = −2.934, se = 0.685, P < .001) were found to be inversely associated with the IIEF-EFD scores. Clinical Implications Advanced age, presence of three-vessel disease, and diabetes mellitus are the indicators of sexual rehabilitation needs in patients after STEMI. Strengths & Limitations This is the first study investigating the predictor variables for the development of ED after coronary artery disease treatment. The limitations include the lack of evaluation of anxiety and depression and the measurements of testosterone levels. Conclusion The prevalence of ED was high among patients with coronary artery disease, and the frequency of ED increased during 3-month follow-up. Advanced age, three-vessel disease, and diabetes were significant predictors of ED with changes in IIEF-EFD score in patients with STEMI who underwent PPCI.