Implantable cardioverter-defibrillator (ICD) in heart failure with reduced ejection fraction (EF) patients reduces risk for sudden cardiac death (SCD). Previous data suggest that the benefit of ICD therapy in real life may be lower than expected from the results of controlled studies and only about one-third of ICD patients receive appropriate therapies. Nevertheless, all ICD patients are at risk of perioperative complications and inappropriate shocks. We retrospectively studied 613 patients undergoing ICD for primary prevention in 2002-2015; we excluded inherited arrhythmogenic syndromes. Patients underwent 12-leads ECG, echocardiography, laboratory tests and quality of life questionnaire. We evaluated comorbidities, appropriate therapies, complications and all-cause mortality. Consecutive patients (age 67 ± 10 years, 81% males, 59% ischaemic aetiology) were followed for 51 ± 31 months. 198 patients (32%) received appropriate ICD therapy, 93 (15%) had inappropriate shocks, 53 (8%) had at least one complication (electrode dysfunction, infection and pocket related) and 191 (33%) died. Multivariate analysis showed atrial fibrillation (OR = 1.8, CI = 1.27 - 2.53; p < 0.01), diabetes (OR = 1.8, CI = 1.27 - 2.53; p = 0.041) and vasculopathy (OR = 1.8, CI = 1.27 - 2.53; p = 0.031) as predictors of appropriate therapy. Logistic regression, considering atrial fibrillation, diabetes, vasculopathy, EF, NYHA class, left atrial diameter and natremia, identified SCD low risk group (probability < 0.1258). Ventricular arrhythmias necessitating ICD therapy are common, but complications and inappropriate therapies are frequent. Many parameters should be considered for a better selection of ICD candidates, to reduce ineffective implants. Our multifactorial score may eventually reduce about 10% ICD implantation.