The present thesis concerns the modification of the Offer Self-Image Questionnaire for Adolescents (OSIQ) and its adaptation to a Greek sample. Three studies are presented which involve the course of development of the modified questionnaire namely the Self-Image Questionnaire for Adolescents (SIQA) and the psychometric properties of its scales. Study I presents a series of exploratory Factor Analyses of the OSIQ, based on the data from 1,314 Greek adolescents aged 13-17 years, which led to a modified version with 89 items and 7 scales. The psychometric properties of the scales are presented. Study II is based on data collected from 423 Greek adolescents aged 13 to 17 years and refers to the description of the 7 scales of the modified questionnaire, the creation of its short version, the internal consistency of the scales of both versions and an ANOVA comparing the parameters of sex, age and socioeconomic status of the subjects with their performance on the scales of both SIQA versions. Study III examines the reliability and validity of both SIQA versions based on the data from a group of 305 normal Greek adolescents and 95 deaf Greek adolescents all aged 13-17 years. Two types of reliability are employed; (a) internal consistency and (b) test-retest. Two methods of validity are also employed; (a) construct validity comparing the SIQA scales with the Coopersmith Self-Esteem Inventory (SEI) scales and (b) discriminant validity comparing normal with deaf adolescents.