This systematic review investigates the carbon footprint (CF) of healthcare systems, focusing on input-output (I–O) based calculations. The review includes 15 studies that calculated and reported the CF of one or more healthcare systems. The mean ratio of healthcare system emissions to total national emissions was 4.9% (1.5%–9.8%), with CFs growing in most countries. Hospital care accounted for the largest share of total CF. At least 71% of the methodological items were reported by each study. The study highlights that healthcare systems significantly contribute to national carbon emissions, with hospitals being a major contributor. Mitigation measures can help reduce emissions over time. The checklist developed here can serve as a reference for future research to ensure methodological transparency and consistency. The review found that most studies used top-down methods, with some employing bottom-up approaches. SRIO models were commonly used for single-country studies, while MRIO models were used for multi-country studies. The number of sectors varied, with MRIO studies typically covering more sectors. CO₂ emissions were the most frequently reported greenhouse gas (GHG), with some studies including other GHGs like methane and nitrous oxide. The results showed that emissions from healthcare systems have been increasing in most countries, except in Scotland and England. The CF of healthcare systems in Japan, Canada, the USA, and Australia has increased over time, with annual increases ranging from 0.7% to 3.8%. The global trend showed an increase in CF of 2.7% per year from 2000 to 2015. The breakdown of emissions showed that hospitals, medical retail, and ambulatory healthcare services contributed the most to the CF of healthcare systems. Scope 3 emissions, which include indirect emissions from activities outside the healthcare system, were the largest contributor. The CF of healthcare systems in different countries ranged from 2.7% in China to 9.8% in the USA. The review identified limitations, including the exclusion of studies in non-English and German languages, potential grey literature, and the lack of standardized reporting. The study recommends further research to assess the effects of emission reduction efforts, examine aggregation errors in I–O methodologies, and analyze methodological differences to guide future research. The transparency checklist developed in this study can serve as a reference for future research to ensure methodological consistency and transparency.This systematic review investigates the carbon footprint (CF) of healthcare systems, focusing on input-output (I–O) based calculations. The review includes 15 studies that calculated and reported the CF of one or more healthcare systems. The mean ratio of healthcare system emissions to total national emissions was 4.9% (1.5%–9.8%), with CFs growing in most countries. Hospital care accounted for the largest share of total CF. At least 71% of the methodological items were reported by each study. The study highlights that healthcare systems significantly contribute to national carbon emissions, with hospitals being a major contributor. Mitigation measures can help reduce emissions over time. The checklist developed here can serve as a reference for future research to ensure methodological transparency and consistency. The review found that most studies used top-down methods, with some employing bottom-up approaches. SRIO models were commonly used for single-country studies, while MRIO models were used for multi-country studies. The number of sectors varied, with MRIO studies typically covering more sectors. CO₂ emissions were the most frequently reported greenhouse gas (GHG), with some studies including other GHGs like methane and nitrous oxide. The results showed that emissions from healthcare systems have been increasing in most countries, except in Scotland and England. The CF of healthcare systems in Japan, Canada, the USA, and Australia has increased over time, with annual increases ranging from 0.7% to 3.8%. The global trend showed an increase in CF of 2.7% per year from 2000 to 2015. The breakdown of emissions showed that hospitals, medical retail, and ambulatory healthcare services contributed the most to the CF of healthcare systems. Scope 3 emissions, which include indirect emissions from activities outside the healthcare system, were the largest contributor. The CF of healthcare systems in different countries ranged from 2.7% in China to 9.8% in the USA. The review identified limitations, including the exclusion of studies in non-English and German languages, potential grey literature, and the lack of standardized reporting. The study recommends further research to assess the effects of emission reduction efforts, examine aggregation errors in I–O methodologies, and analyze methodological differences to guide future research. The transparency checklist developed in this study can serve as a reference for future research to ensure methodological consistency and transparency.