The existential theory of radical mid-life career change is a theory focusing on work salient individuals around the age of 35 and beyond who have previously established a career path and who are in a position to alter that path due to minimal environmental constraints. The theory postulates that at around this age the realization of the finite quality of one's life begins to intrude into consciousness. As a response to this intrusion, each individual implicitly or explicitly chooses to deny the existence of these thoughts and their implications or to engage in a process of coming to terms with personal mortality and its significance to the remaining years of life. Choosing an acceptance strategy results in a fundamental change in one's self-concept which leads to a life evaluation process. Subsequent to the life evaluation process is an occupational evaluation process which leads to a judgment of its congruence or incongruence with the reformulated self-concept. If one concludes that the present occupation is congruent with the reformulated self-concept, stability of the established career path is predicted. Conversely, a conclusion of incongruence of the present occupation with the amended self-definition produces an internal motivation towards congruence resulting in a radical career change. The implications of this theory for assisting voluntary mid-life career clients seem appropriate within the context of extant empirical evidence. (ABL)