This article presents the process and the effects of individual psychotherapy conducted in the prison, on a patient addicted to alcohol and drugs. The psychotherapy was based on the ideas of existential analysis (Frankl, Längle). This is the first case of applying this method in prison isolation conditions in Poland. The therapy was focused on symptoms of addiction and fundamental existential motivations. Building a good therapeutic relationship in the difficult prison background was an essential part of the healing process. As a result, the ex-patient has kept abstinence from psychoactive substances and has not committed any crime to the present day (since seven years from the end of therapy). He has lived according to his newfound authentic values and has experienced fulfilment. The presented case illustrates that existential analysis creates a possibility of comprehensive work on the whole addicted person’s psychological and spiritual problems and can be applied as an effective tool in the process of resocialisation.