In the field of teacher attrition, there is a significant body of literature on why teachers leave high-needs urban schools and particularly why beginning teachers leave their schools and the profession. However, there is little research on the reasons why experienced teachers leave the teaching profession. This paper examines this subject by considering whether teachers experience an "identity crisis" in their careers which prompts them to leave. Drawing on identity theory, data from a single case study of an experienced urban teacher are taken from a wider qualitative research study carried out in London, England. The case is made that decisions to leave or stay in a school are contingent on a number of personal, professional and situational factors related to the teacher's identity. The article concludes that one way to understand why long-serving teachers leave the profession is to examine aspects of their teacher identity and explore how a crisis in professional identity can contribute towards teacher attrition. In the light of this alternative approach towards understanding attrition, at the very least, supportive structures can be put in place to encourage more teachers to stay and contribute to the success and well-being of children from disadvantaged backgrounds.