The Experiencing of Self Scale (EOSS) was created for the evaluation of Functional Analytic Psychotherapy (Kohlenberg & Tsai, 1991, 2001, 2008) in relation to the concept of the experience of personal self as socially and verbally constructed. This paper presents a reliability and validity study of the EOSS with a Spanish sample (582 participants, 18 to 70 years old; 198 men and 384 women), gathered from different cities, universities and clinical centers. The clinical sample consisted of 162 people undergoing psychological or psychiatric treatment and 420 people without problems. Standard questionnaires (Eysenk Personality Questionnaire-Revised, Rosenberg Self-Esteem and Dissociative Experiences Scale) which measure similar self-concepts were used to explore the validity of the EOSS. The results show high internal reliability (Cronbach's alpha = 0.935) and both high and significant correlations with the "neuroticism" scale of the EPQ-R (0.212, p less than 0.001), "dissociation" of the DES (r = 0.483, p less than 0.001) and negative self-esteem of the RSES (r = -0.544, p less than 0.001). The partial and total scores of EOSS also differentiated the clinical sample with high scores from the standard sample (t = 7.78, p less than 0.001). In conclusion, the EOSS has high internal reliability, high validity with similar self-concept scales, and it is also useful for evaluating people with psychological problems of self. (Contains 4 tables.)