Sudden cardiac death (SCD), mainly caused by ventricular arrhythmias, is one of the leading causes of mortality in adult congenital heart disease (ACHD) patients. An implantable cardioverter defibrillator (ICD) may prevent SCD, but risk stratification remains challenging. In this review, we will address the current guideline recommendations for ICD implantation in ACHD patients, as well as review a recent study in which the discriminative ability for SCD of these guidelines is evaluated. In this study, the guideline recommendations were applied to patients who died of SCD and living controls. Among SCD cases, 35%-41% of patients were recommended ICD, whereas 16%-17% of controls were recommended ICD. The discriminative ability for SCD of the guidelines was poor, with an area under the receiver operating characteristic curve of 0.61-0.63. Risk stratification for SCD in ACHD patients, therefore, remains to be a work-in-progress.