The aim of this study was to examine the relationship between the use of Instagram (active and passive use), social comparison, and body image in adolescents, as well as the relationship between viewing different content on Instagram and body image. The research involved 189 adolescents, specifically high school students in Rijeka and Pula. A questionnaire for examining the use of Instagram was constructed for the purposes of this research. The Body Shape Questionnaire (BSQ) was used as the measure of body dissatisfaction, and selected and adapted items of the Motivations for Electronic Interaction Scale (MEIS) were used as the measure of social comparison. A statistically significant positive correlation was found between the frequency of passive use of Instagram and body dissatisfaction, as well as social comparison. Frequency of active Instagram use was also positively associated with body dissatisfaction, while no association with social comparison was found. Hierarchical regression analysis, controlling for gender and BMI, showed that social comparison and passive Instagram use are significant positive predictors of body dissatisfaction, while the frequency of active use of Instagram was not a significant predictor. Additionally, a mediating effect of social comparison was found in the relationship between the frequency of passive use of Instagram and body dissatisfaction. Finally, the results showed a significant positive association between the frequency of viewing profiles related to healthy eating and fitness and body dissatisfaction, while viewing profiles of peers/family and public figures was not associated with body dissatisfaction. These results partially confirmed the set hypotheses and were explained by previous research, theoretical models and methodological limitations of this study.