BACKGROUND: Higher incidence of acute coronary syndrome (ACS), among those with lower income, has been recognized in the most recent decades. Still, there is a paucity of data on temporal changes. This study aims to investigate 20-year time trends in income-related disparity in the incidence of ACS in Denmark. METHODS: This Population-based repeated cross-sectional study included all patients with first-time ACS, aged ≥20 years, registered in the Danish National Patient Registry 1998-2017. Aggregated sociodemographic data for the Danish population was accessed from Statistics Denmark. Yearly incidence rates (IR) and incidence rate ratios (IRR), with the highest-income quartile as a reference, were standardized using cell-specific personal equivalent income according to year, sex and age group with 95% confidence intervals. Interaction analysis was executed for differences in IR of ACS between the lowest- and highest-income quartile over time. RESULTS: A total of 220 070 patients hospitalized with ACS from 1998 to 2017 were identified. The yearly standardized ACS IRs decreased in all income quartiles. However, the IR remained higher in the lowest-income quartile compared to the highest for both men [1998: IRR 1.45 (95% confidence interval, CI 1.39-1.52) and 2017: 1.47 (1.40-1.54)] and women [1998: IRR 1.73 (1.64-1.82) and 2017: 1.76 (1.65-1.88)]. Interaction analysis showed that over the period the difference in IR between the lower- and the highest-income quartile decreased with 1-5 ACS cases per 100 000 person-year. CONCLUSION: Income-related disparity in the incidence of ACS was present in Denmark between 1998 and 2017. Despite a marked overall decrease in the yearly ACS incidence, the extent of income-related disparity remained unchanged.