Patients with diabetic nephropathy face an increased risk of dying due to cardiac causes. The aim of this follow-up trial was to describe the association between the length of the QT interval, as a marker of myocardial electrical stability, and the risk of death in insulin-dependent (IDDM) diabetic patients with overt diabetic nephropathy. A consecutive sample of 85 IDDM patients with overt diabetic nephropathy (i.e. persistent proteinuria > or = 500 mg/24 h) were followed-up until death or for a period of 5-13 years. QT intervals were measured once at baseline in a 12-lead ECG and corrected for heart rate (QTc). During the follow-up period 33 patients (39%) died. In the Cox proportional hazards model independent predictors of death were age (p = 0.0007), the length of the maximum QTc period (p = 0.0049), presence of autonomic neuropathy (p = 0.0068), diabetes duration (p = 0.0163) and RR variation (p = 0.0395). In conclusion, in nephropathic IDDM patients QT prolongation is associated with an increased mortality risk which is independent of the presence of autonomic neuropathy. Further studies are needed to determine whether this risk might be reduced by therapeutic interventions.