In everyday life can be perceived some typical attitudes of individuals, which can be described as excessive self-confidence. It is about self-esteem that does not match with a realistic appraisal of their own characteristics and abilities and skills in different areas of life. To attempt to theoretically explain over-confidence, we started from the assumptions that make psychoanalysis (the defense mechanisms of the personality), and the concept of over-estimation of the accuracy of solving the set tasks ("overconfidence"). The aim of the research was to determine whether the relatively unique set of interrelated characteristics that could be described as self-sufficiency exist. For this purpose, the occasional sample of 197 respondents of both genders is tested. The subjects in sample had heterogeneous occupations and levels of education. The preliminary version of the Overconfidence Questionnaire for measuring this hypothetic construct was applied. The Questionnaire showed satisfactory reliability. Also, we have found that the dimensions of the questionnaire differ significantly the respondents in relation to their gender but not in realtion to education. The dimensions were not significantly associated with demographic variables. The questionnaire has shown satisfactory metric characteristics. The possibility of applying the construct in the sport and the guidance for future researches were given.