Objective: The aim of this project is to assess methadone treatments in Andalusia. This paper introduces some of the results of the pilot study. Methods: Retrospective review of a sample of 60 patients admitted for treatment from 1/1/98 in three Provincial Drug Dependency Centres. Results: To estimate the principal outcome variable – the retention rate – two criteria were used to define censored and events. Thus, two survival curves were achieved which showed retention at 18 months of 75% and 53.3% respectively. Conclusions: The results of the use patterns and serological state in respect of HIV are positively evaluated. The difference between the survival curves (21.7%) shows the importance of the criteria used to define censored and event cases in the main variable to determine the success/failure of a Methadone Treatment Programme. Even so, the retention observed supports the perception of a good ability of these treatments in Andalusia to retain their patients. However, we must wait for the final results. The high percentages of “unknown� data suggest important deficiencies in the level of knowledge that can be obtained as well as the possibility of carrying out continuous assessments with retrospective information.