The association of non-thyroidal illness syndrome (NTIS) and hypothyroidism with the prognosis in ischemic heart disease (IHD) population is inconclusive.We aimed to evaluate the influence of NTIS and hypothyroidism on all-cause mortality and major adverse cardiac events (MACE) in IHD population.We searched PubMed, EMBASE, Scopus, Web of Science, and Cochrane Library from inception through February 17, 2020.Original articles enrolling IHD patients, comparing all-cause mortality and MACE of NTIS and hypothyroidism with those of euthyroidism, and providing sufficient information for meta-analysis were considered eligible.Relevant information and numerical data were extracted for methodological assessment and meta-analysis.Twenty-three studies were included. The IHD population with NTIS was associated with higher risk of all-cause mortality [hazard ratio (HR)=2.61; 95% confidence interval (CI)=1.89-3.59] and MACE (HR=2.22; 95% CI=1.71-2.89) than that without. In addition, the IHD population with hypothyroidism was also associated with higher risk of all-cause mortality (HR=1.47; 95% CI=1.10-1.97) and MACE (HR=1.53; 95% CI=1.19-1.97) than that without. In the subgroup analysis, the ACS subpopulation with NTIS was associated with higher risk of all-cause mortality (HR=3.30; 95% CI=2.43-4.48) and MACE (HR=2.19; 95% CI=1.45-3.30). The ACS subpopulation with hypothyroidism was also associated with higher risk of all-cause mortality (HR=1.67; 95% CI=1.17-2.39).The IHD population with concomitant NTIS or hypothyroidism was associated with higher risk of all-cause mortality and MACE. Future research is required to provide evidence of the causal relationship, and to elucidate whether normalizing thyroid function parameters can improve prognosis.