Comorbidity is a central aspect in current psychopathology. In the field of the drug addictions, different studies have shown a high prevalence of personality disorders in this population. The goal of the present investigation was centered on analyzing the relation between different personality disorders and the relapses during the therapy. Also, the degree of fulfilment of different therapeutic instructions of these patients was studied. The results obtained indicate the presence of high rates of relapses in subjects with serious personality disorders as well as less fulfilment of therapeutic instructions. The diagnostic and therapeutic implications of these results are discussed.