Functional Analytic Psychotherapy (FAP) offers a radically behavioral and transdiagnostic conception of the formation of the “self” and the appearance of a diversity of psychological problems. This study examined the extent to which a wide variety of psychological disorders (somatization, obsessive–compulsive, interpersonal sensitivity, depression, anxiety, hostility/aggressiveness, phobic anxiety, paranoid ideation, and psychoticism) and a global index of psychopathological severity may in fact be linked to problems of the “self” according to the FAP conception. Two questionnaires, one related to self-experience according to FAP and the other to find the scores on several different psychopathology scales, were administered to 280 adult Spaniards for this purpose. The results confirmed the transdiagnostic nature of the “self”-experience. There are significant and strong correlations between all the psychopathology scales studied and self-experience. Linear regression analyses also show that, along with age and gender, in some cases, the score on self-experience predicts each and every one of the psychopathological variables studied, in addition to the Global Severity Index. These results are discussed and related to the transdiagnostic approach to psychopathology.