STUDY OBJECTIVE--To identify geographical differences in coronary heart disease (CHD) attack rates in a small urban area and to relate these to indicators of socioeconomic class. DESIGN--CHD attack rates were calculated from data of the Ghent MONICA myocardial infarct register for the period 1983-87. The city of Ghent is subdivided into 201 sectors based on morphological, and socioeconomic characteristics. During the national census of 1981, the main determinants of residential differentiation were measured. These sector variables were linked with the CHD attack rates. PATIENTS--All residents of the city aged 25-69 years are prospectively followed with regard to heart attacks. Between 1982 and 1987, 1728 suffered an acute heart attack according to MONICA criteria. MAIN RESULTS--Significant (p < 0.05) differences in age and sex standarised attack rates were observed between city sectors. These differences were related to an index of socioeconomic status. CONCLUSION--Within a small urban area, significant geographical differences occur in CHD attack rates and these are related to socioeconomic status.