INTRODUCTION: Treatment dropout is an unsolved problem in the addiction process which makes frequent the failure of the addiction therapy. Research shows that the majority of dropouts occur during the first weeks of the treatment. These are the most serious ones because they have the worst prognosis. Some factors, related to the patients and the therapy, have been associated with treatment dropout but the diversity of studied variables, the heterogeneity of patients and the sparse population of many studies, hampers external validity and comparison of results.