This paper explores what is perhaps the most important contribution of Harry Guntrip to psychoanalysis: namely his concept of the "regressed ego." In the course of his psychoanalytic work, he found certain concepts to be problematic. Therefore, while he valued some of Freud's ideas, he challenged his emphasis upon the importance of the instincts. Guntrip then drew extensively on the more object relational approach of Fairbairn and Winnicott. Nevertheless, although Guntrip believed that all these figures described important dimensions of psychological experience, he felt that they failed to acknowledge that layer which he called the "regressed ego." In his analysis of the "regressed ego," Guntrip made a valuable contribution to psychoanalytic theory and practice. However, because he thought that with this idea he had discovered the underlying cause of most psychological disturbances, he engaged in a form of reductionism and therefore undermined the value of his observations about this layer of psychological experience.