Elevated serum levels of parathyroid hormone (PTH), one of the main regulators of calcium homeostasis and vitamin D metabolism, have been proposed as predictors of mortality. The impact of T2DM on the putative association between PTH and mortality has not been investigated thus far.The aim of our study was to investigate the impact of T2DM on the power of PTH to predict mortality risk.Serum PTH levels were determined in 904 consecutive Caucasian patients referred to coronary angiography for the evaluation of established or suspected stable coronary artery disease (CAD), including 235 patients with T2DM. Prospectively, deaths were recorded over a mean follow-up period of 6.3 years.PTH at baseline did not differ significantly between patients with and without T2DM (P=0.307). Cox regression analysis revealed that the serum PTH level strongly predicted all-cause mortality in patients with T2DM (HR=2.35 [1.37-4.03]; P=0.002), whereas PTH did not predict all-cause mortality in patients without T2DM (HR=1.04 [0.81-1.32]; P=0.766). The interaction term PTH x T2DM was significant (P=0.006), indicating a significantly stronger impact of PTH on mortality risk in patients with T2DM than in individuals without diabetes. The impact of PTH on mortality risk in patients with T2DM remained significant after adjustment for HbA1c, diabetes duration, classical cardiovascular risk factors, serum levels of vitamin D and kidney function (HR=2.10 [1.10-4.10]; P=0.030).We conclude that PTH is a significantly stronger predictor of all-cause mortality in patients with T2DM than in those without T2DM.