The high drop-out rate in treatment programs is one of the most important problems in the area of drug addictions. This study evaluated the effect of the use of incentives on retention in an outpatient program for cocaine addicts. The effect of individual variables on program drop-out was also analysed. Participants were 66 subjects who were randomly assigned to one of three treatment groups: standard treatment, treatment with incentives I, and treatment with incentives II. The patients of these two groups received incentives contingent on cocaine abstinence with two different magnitudes. Retention rate at six months was 35% in the standard treatment, 78.6% in the treatment with incentives I, and 53.3% in the treatment with incentives II. The global prognostic capacity of the individual variables (sociodemographic, history and consumption pattern, psychopathological variables, and EuropASI scores) was 85.7%, with the psychopathological variables being more closely related to retention. These results suggest that the use of incentives may be an effective strategy to improve retention in outpatient treatments for cocaine addiction.