BACKGROUND: The objective of this study was to assess the methodological quality and clarity of reporting of the systematic reviews (SRs) supporting clinical practice guideline (CPG) recommendations in the management of ST-elevation myocardial infarction (STEMI) across international CPGs. METHODS: We searched 13 guideline clearinghouses including the National Guideline Clearinghouse and Guidelines International Network (GIN). To meet inclusion criteria CPGs must be pertinent to the management of STEMI, endorsed by a governing body or national organization, and written in English. We retrieved SRs from the reference sections using a combination of keywords and hand searching. Two investigators scored eligible SRs using AMSTAR and PRISMA. RESULTS: We included four CPGs. We extracted 71 unique SRs. These SRs received AMSTAR scores ranging from 1 (low) to 9 (high) on an 11-point scale. All CPGs consistently underperformed in areas including disclosure of funding sources, risk of bias, and publication bias according to AMSTAR. PRISMA checklist completeness ranged from 44% to 96%. The PRISMA scores indicated that SRs did not provide a full search strategy, study protocol and registration, assessment of publication bias or report funding sources. Only one SR was referenced in all four CPGs. All CPGs omitted a large subset of available SRs cited by other guidelines. CONCLUSIONS: Our study demonstrates the variable quality of SRs used to establish recommendations within guidelines included in our sample. Although guideline developers have acknowledged this variability, it remains a significant finding that needs to be addressed further. FUNDING: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.