Background: The value of an implantable cardioverter defibrillator(ICD) for primary prevention in dilated cardiomyopathy(DCM) is unclear, as randomized trials could not show a survival benefit compared to drug therapy. It has not been investigated if patients with a very poor left ventricular function(LVEF) could profit from an ICD. Methods: Consecutive patients with DCM who received an ICD between December 1996 and November 2003 were included in this analysis. Patients were divided in group A(secondary prevention) and group B(primary prevention). Both groups were stratified in subgroups with left ventricular ejection fraction(LVEF) below and above 20% . Results: Fifty eight patients were included(male 50, age 56.4± 12.7 years). Follow-up was 34± 19 months. There was no difference regarding death(18% vs. 11% ), but significant differences(p value< 0.05) regarding any adverse events(55% vs. 22% ), any ICD intervention(48% vs. 17% ) and ICD interventions for life-threatening arrhythmias(27% vs. 0% )between group A and B. LVEF was not predictive for events in group A, whereas in group B only patients with a LVEF< 20% had events(p value 0.02). Over time there was an increase of the LVEF of more than 15% determined by echocardiography in 36% of patients, significantly more often in group B. Conclusions: Indication for primary prevention with an ICD in DCM should be made with caution. Larger studies are needed to determine if patients with LVEF of< 20% might benefit from an ICD. Background: The value of an implantable cardioverter defibrillator (ICD) for primary prevention in dilated cardiomyopathy (DCM) is unclear, as randomized trials could not show a survival benefit comparable to drug therapy. It has not been investigated if patients with a very poor left Methods: Consecutive patients with DCM who received an ICD between December 1996 and November 2003 were included in this analysis. Patients were divided in group A (secondary prevention) and group B (primary prevention) Both groups were stratified in subgroups with left ventricular ejection fraction (LVEF) below and above 20%. Results: Fifty eight patients were included (male 50, age 56.4 ± 12.7 years). Follow-up was 34 ± 19 months. There was no difference regarding death (18% vs. 11%), but significant differences (p value <0.05) on any adverse events (55% vs. 22%), any ICD intervention life-threatening arrhythmia (27% vs. 0%) between group A and B. LVEF was not predictive for events in group A, but in group B only patients with a LVEF <20% had events (p value 0.02). Over time there was an increase of the LVEF of more than 15% determined by echocardiography in 36% of patients, significantly more often in group B. Conclusions: Indication for primary prevention with an ICD in DCM should be made with caution. Larger studies are needed to determine if patients with LVEF of <20% might benefit from an ICD.