Background: Both diabetes mellitus (DM) and coronary artery spasm (CAS) are associated with endothelial dysfunction. Thus, a higher incidence of CAS is expected in diabetic patients (pts). We evaluated the impact of diabetes on CAS with intracoronary acetylcholine (ACh) provocation test. Methods: A total 986 pts (106 DM versus 880 non-DM pts) with angiographically normal coronary artery received ACh provocation test. Using propensity score, we reassembled 2 well matched cohorts (106 diabetic versus 106 non-diabetic pts). ACh was injected into left coronary artery in incremental doses of 20, 50 and 100關g/min. Significant CAS was defined as a transient >70% luminal narrowing with concurrent chest pain and/or ST-segment changes. Blood sugar and HbA1c were determined in diabetic pts. HbA1c < 7% was considered controlled blood sugar level. Results: The incidence of CAS were similar between DM pts versus non-DM pts (39.6% vs 41.5%, P=0.780). The angiographic characteristics of CAS were also similar between the two groups. Subgroup analysis in DP pts showed that the incidence of CAS were similar between patients with versus without controlled blood sugar levels (43.8% vs 36.2%, P=0.429). Multivariate analysis controlling the baseline biases of age and sex showed that the controlled blood sugar level was not an independent predictor for CAS (odd ratio 1.06, 95% confidence interval 0.46-2.44, P=0.895). Conclusions: Despite the expected endothelial dysfunction, diabetes and the status of blood sugar control are not associated with CAS, suggesting the different mechanisms and risk factors may contribute the development of significant CAS.