The present work attempts to show, through a case study, the possibilities of Acceptance and Commitment Therapy (ACT) applied from existential thought. First of all we describe the symptoms referred to by a patient diagnosed as suffering from “negative schizophrenia”. These symptoms are then analyzed in existential terms, with special emphasis on the notion of “personal identity”. This is followed by a description of the intervention carried out applying the techniques and principles of ACT, and an account of the patient’s evolution over two years. Finally, we defend the appropriateness of acceptance in problems of an existential nature, at the same time as arguing for situating people’s difficulties in a vital more than purely psychological framework.