Aim. To compare Five-Factor personality traits in patients maintaining abstinence and relapsed patients (i.e. those who relapsed within a year after treatment), following eight weeks of in-house treatment and three months of out-patient treatment. Method. In longitudinal studies, a sample of 190 patients was analysed (49 females and 141 males; mean age: 43). The patients participated in therapeutic programmes at several addiction treatment centres across Poland. Personality traits were measured using the NEO PI-R inventory proposed by Costa and McCrae (adapted into Polish by Jerzy Siuta) at the initial stage of the treatment. Abstinence was assessed based on the interview. Results. As far as the main traits are concerned, abstinent patients have higher levels of Agreeableness and Conscientiousness than patients who relapsed within a year following the therapy. Moreover, they are characterised by higher levels of constituent traits: Straightforwardness, Ideas and Altruism, as well as higher levels of Order, Self-Discipline and Dutifulness. However, their levels of Hostility are lower compared to patients not maintaining abstinence. Conclusions. After one year follow-up, the group maintaining abstinence is characterised by a higher Agreeableness and Conscientiousness, which is beneficial for cooperation with others as well as undertaking and realising tasks. Moreover, lower constituent values of Neuroticism are linked to higher adaptability and greater therapy participation than in a relapsed group. An early identification of patients bearing traits linked to lower adaptability will decrease the possibility of relapse thanks to making a greater effort at enhancing treatment participation while paying special attention to any co-existing psychopathology.