Background: An anti-smoking attitude should be established among adolescents with T1DM and adolescents' smoking outcome expectations, anti-smoking self-efficacy levels, and social anxieties should be determined. Objectives: This study was carried out with the aim of to investigate the effects of social anxiety levels and self-efficacy perceptions of adolescents with T1DM on smoking outcome expectations. Methods: This study used a descriptive, correlational, and cross-sectional design. The researchers have complied with the guidelines of STROBE Checklist in presenting this studyThis study was conducted in Izmir, Turkey, with 210 adolescents diagnosed with T1DM who were registered at the pediatric endocrinology outpatient clinics of hospitals and were selected using the convenience sampling method between January and December 2019. Results: A significant relationship was found between self-efficacy and positive smoking expectation (r = 0.01) and anti-smoking (r = 0.57); between social anxiety and smoking r = (-0.05) and negative smoking expectation (r = 0.05). Also, a significant relationship was found between self-efficacy and anti-smoking (r = 0.57) and between social anxiety and anti-smoking (r = -0.05). Conclusion: Adolescents with high levels of self-efficacy had negative perceptions of smoking, therefore they had high negative smoking outcome expectations.