AIMS: Identification of patients most likely to benefit from implantable cardioverter defibrillator (ICD) implant remains a complex challenge. This study aimed to investigate the utility of measures derived from standard 10 s 12-lead electrocardiogrphy (ECG) without complex signal processing in predicting appropriate therapy in an ICD population. METHODS AND RESULTS: We examined 108 ICD patients for primary (n = 32) and secondary prevention (n = 76). Baseline clinical data and characteristics of QRS complex, T-wave, and heart rate from standard 12-lead ECG were examined and related to the occurrence of subsequent appropriate therapy. Over a mean follow-up of 29 +/- 11 months, 44% of patients received appropriate therapy. Patients with depressed heart rate variability (HRV) (</=6.5%) were 2.68 [95% confidence interval (CI) 1.21-5.90, P = 0.015] times more likely to receive appropriate therapy than patients with HRV >6.5%. In patients with bundle branch block (BBB), large QRS dispersion of >39 ms was associated with 2.88 times risk (95% CI 1.24-6.71, P = 0.014) of experiencing appropriate therapy than those with QRS dispersion <39 ms. In patients without BBB, reduced maximum T-wave amplitude (<0.4 mV) were 3.82 times (95% CI 1.63-8.93, P = 0.002) more likely to receive appropriate therapy compared with those with maximum T-wave amplitude >0.4 mV. History of atrial arrhythmia [hazard ratio (HR) = 2.30, 95% CI 1.29-4.12, P = 0.005] and secondary prevention (HR = 2.55, 95% CI 1.14-5.71, P = 0.022) were also predictive of device therapy. CONCLUSION: Measurements from standard 12-lead ECG were predictive of appropriate therapy in a heterogeneous ICD population. Incorporation of 12-lead ECG parameters such as these into risk stratification models may improve our ability to select patients for ICD implantation.