BACKGROUND: Alcoholism is a progressive neurocognitive developmental disorder. Recent evidence shows that computerized training interventions (Cognitive Bias Modification, CBM) can reverse some of these maladaptively changed neurocognitive processes. A first clinical study of a CBM, called alcohol-avoidance training, found that trained alcoholic patients showed less relapse at one-year follow-up than control patients. The present study tested the replication of this result, and questions about mediation and moderation. METHODS: 509 alcohol-dependent patients received treatment as usual (primarily Cognitive Behavior Therapy) inpatient treatment. Before and after treatment, the implicit approach bias was measured with the Alcohol Approach-Avoidance Task. Half of the patients were randomly assigned to CBM, the other half received treatment as usual only. Background variables, psychopathology and executive control were tested as possible moderating variables of CBM. One year after treatment, follow-up data about relapse were collected. RESULTS: The group receiving CBM developed alcohol-avoidance behavior and reported significantly lower relapse rates at one-year follow-up. Change in alcohol-approach bias mediated this effect. Moderation analyses demonstrated that older patients and patients with a strong approach-bias at pretest profited most from CBM. CONCLUSIONS: CBM is a promising treatment add-on in alcohol addiction and may counter some of the maladaptive neurocognitive effects of long-term alcoholism.