BACKGROUND Millions of adolescents are facing the burden of malnutrition in India, and the sociocultural context of nutrition poses challenges while addressing this burden. This study aimed to assess: (a) the determinants of knowledge, attitude, and self-efficacy scores and (b) the relationships between nutrition-related knowledge, attitude, and self-efficacy scores among adolescents in India. METHODS The community-based study was conducted among adolescents across three rural and three urban districts in India. This observational study employed a self-administered structured questionnaire containing information on demography, nutrition-related knowledge, attitude, and dietary self-efficacy. Differences in knowledge, attitude, and self-efficacy scores between sociodemographic variables were assessed using the t-test. Regression analysis was used to determine relationships between knowledge, attitude, and self-efficacy scores. RESULTS A total of 985 adolescents (44.5%) from rural areas and 1225 (55.5%) from urban slums participated. There were significant differences in knowledge, and self-efficacy scores between rural, urban inhabitants (P < 0.001), and adolescents with different grades of education (P < 0.001 for knowledge and P = 0.01 for self-efficacy). There were significant differences in knowledge and attitude scores among adolescents from non-backward and backward classes (P < 0.001 for knowledge and P = 0.02 for attitude) and those who were vegetarians and non-vegetarians (P = 0.002 for knowledge and P < 0.001 for attitude). The study demonstrated significant relationships between knowledge, attitude, and self-efficacy scores (P < 0.001). CONCLUSIONS Nutrition-related knowledge, attitude, and self-efficacy scores are determinants of dietary behavior and are inter-related. Community-based interventions targeting to improve the nutritional status of adolescents should focus on improving self-efficacy besides the other two determinants.