Several works have been reported diabetes as an independent risk factor for ischaemic heart disease. The use of different methodologies have been an obstacle to a comparison of these studies. The study realized has sought to test the association between diabetes and ischaemic heart disease, after adjusting for known confounders and/or modifiers of effect. The study was designed as a case control study and the period of data collection was one year (March/93 to February/94). The cases were compared with three kinds of controls in two base-populations: primary and secondary. The sample was composed of 833 individuals of both genders of 30-69 years of age living in the city of S. Paulo, Brazil. Logistic regression was the statistical method used for the analysis of the data. The results showed that diabetes was not an independent risk factor for IHD. Hypertension, hypercholesterolemia, smoking and family antecedents of cardiovascular diseases were considered major risk factors for ischaemic heart disease. The interaction between diabetes and exposure levels of the others variables did not present statistical significance. Some methodological issues are presented to explain different magnitudes of effect according to the different kinds of controls. It is concluded that the presence of major risk factors in the models contributed to the disappearance of the association between diabetes and ischaemic heart disease.