We investigated the efficacy of exercise stress thallium in the diagnosis of coronary artery disease in patients with diabetes mellitus. Forty-three patients with known diabetes and suspected of having coronary artery disease were included in the study. All the patients underwent coronary angiography, 24 had significant coronary artery stenosis and 19 had normal coronaries. Out of the 24 patients with a positive angiographic finding, thallium scintigraphy was positive in 21 patients (sensitivity, 87.5%); and false negative in only three of the 24 patients. Out of the 19 patients with normal angiography findings, 16 patients had a normal thallium scan (specificity, 84.2%) and the remaining three had a positive thallium scan. This gives thallium scintigraphy a positive predictive value of 87.5% and negative predictive value of 84.2% when compared with coronary angiography. The findings of this study suggest that stress thallium scintigraphy is a useful modality in screening of coronary artery disease in diabetic patients.