The treadmill exercise score has been used to stratify patients into low-, moderate-, and high-risk groups. This score is derived from ST segment depression, angina, and exercise duration. To determine the coronary arteriographic and exercise thallium perfusion correlates of the score, we examined the extent of coronary artery disease and exercise single photon emission computed thallium-201 results in 834 patients for whom cardiac catherterization data were available. Of those, 174 had no coronary artery disease, 195 had one-vessel, 246 had two-vessel, and 219 had three-vessel disease. Based on the treadmill exercise score, 369 were in the low-risk, 384 in the moderate-risk, and 81 in the high-risk group. The extent of coronary artery disease was 2.1 ± 1 diseased vessels in the high-risk, 1.7 ± 1 in the moderate, and 1.4 ± 1.1 in the low-risk group (p < 0.01). The extent of the thallium abnormality (maximum number of abnormal segments 120/patient) was 10 ± 6 in the high-risk, 7 ± 6 in the moderate, and 6 ± 5 in the low-risk group (p < 0.05). Based on the extent of coronary artery disease and results of thallium imaging, patients were reclassified into three groups: group 1 had three-vessel disease and/or ≥10 abnormal segments (n = 387), group 3 had no coronary artery disease or one-vessel disease and less than five abnormal segments (n = 212), and the remaining patients were in group 2 (n = 235). Patients in group 1 constituted 57% of the patients in the high-risk, 36% in the moderate-risk, and 20% in the low-risk treadmill exercise groups (p < 0.0001). Concordance between the treadmill exercise score and the coronary artery disease/thallium grouping was seen in only 273 patients (33%). Thus, although the mean coronary artery disease score and the thallium score differ in different treadmill exercise score risk groups, considerable overlap exists. It is important to note that patients in the low-risk group may have extensive coronary artery disease or thallium abnormalities, and patients in the high-risk group may be normal or have mild coronary artery disease or a mild thallium abnormality. © 1992.