A total of 69 adolescents, 21 with diabetes mellitus type-1 (DM), 24 with rheumatoid arthritis (RA), and 24 controls matched for sex, age, social background, and living environment, were compared by means of their school grades and the Offer Self-Image Questionnaire. The ages of the children at the time of the diagnosis of the disease and its subsequent duration were the same in the DM and the RA groups. Results show that the academic achievement of adolescents with DM who are well balanced and adolescents with RA with mild or moderate symptoms are equal to those of their healthy peers. In the OSIQ scales there were no statistically significant differences between the groups. In the groups of controls, there were more significant correlations between the OSIQ scores and the school grades than those with the DM or RA adolescents. The direction was positive. The correlations of the 3 groups did not differ significantly from each other. In case of adolescents with various kinds of chronic diseases, it is important to support their motivation for learning and planning the future.KEY WORDS: chronic disease; diabetes mellitus; rheumatoid arthritis; self-image; academic achievement.