BACKGROUND: In Denmark, as in many other Western countries, a decline in mortality from ischaemic heart disease (IHD) has been observed. The present study assesses whether the decline in IHD mortality is due to a decrease in incidence and/or case-fatality, and whether parallel changes occurred in the various manifestations of IHD requiring hospitalization. METHODS: The National Patient Register of hospital discharges and the Causes-of-Death Register were linked and all cases of first admission for IHD including AMI and fatal first manifestations of IHD since 1977 in the entire Danish population were identified. Cases of AMI and IHD were considered as incident cases if no admission for these diagnoses had occurred during the preceding 5 years. Sex-specific, age-standardized annual mortality, incidence and case-fatality rates of AMI (ICD8 code 410), narrowly defined IHD (NIHD, ICD8 codes 410-4) and broadly defined IHD (BIHD, ICD8 codes 410-4, 427 and 795-6) were calculated for the period 1982-1992. RESULTS: During the entire period the age-standardized mortality of AMI, NIHD and BIHD decreased in both men and women. The incidence of AMI and NIHD decreased, while the incidence of BIHD remained constant. Case fatality of AMI decreased in both men and women, while case fatality of NIHD and BIHD decreased in men and in women aged 0-64 years only. CONCLUSION: The declining mortality from IHD in Denmark may be partly due to declining incidence as well as declining case fatality, but changes in disease manifestation or diagnostic drift may also contribute because more broadly defined diagnostic groups showed less or no decline in incidence.