Background: Although the Synergy between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery (SYNTAX) score is used to characterize coronary anatomy based on 9 anatomic criteria such as lesion location and complexity, the relationship between SYNTAX score and myocardial ischemia has yet to be elucidated. Methods and Results: A total of 158 consecutive patients with suspected or known coronary artery disease (CAD), who underwent both ^99mTc-sestamibi single-photon emission computed tomography (SPECT) and coronary angiography, were evaluated. Stress SPECT was assessed using a 17-segment model, and the percentage of the myocardial defect scores (DS) was calculated. In 37 patients with intermediate-high SYNTAX scores (>22), the number of men and the prevalence of multi-vessel CAD were significantly higher, and the % stress and ischemic DS were significantly greater than in 121 patients with low SYNTAX scores (≤22). Coronary risk factors, however, were similar between the 2 groups. The % stress and ischemic DS significantly correlated with SYNTAX score. In patients with a low SYNTAX score, % stress and ischemic DS also significantly correlated with the SYNTAX score, whereas no such correlation was observed in the intermediate-high SYNTAX score group. Conclusions: SYNTAX score correlated well with myocardial ischemia as assessed on stress SPECT in general. The higher the SYNTAX score, however, the less clear was the correlation with the extent of myocardial ischemia.  (Circ J 2013; 77: 2772–2777)