The main objective of this study was to determine the effects of dietary pattern and body mass index on the academic performance of in-school adolescents in Ekiti State. One hundred and twenty eight students (10-19 years) selected from three senior secondary schools in Ekiti State Nigeria, formed the participants for this study. Questionnaire was the instrument for data collection and the data were subjected to descriptive and inferential statistics (bivariate Pearson correlation analysis and linear regression) using Spss version 12 at 0.05 level of significance. Findings of this study showed that of all the adolescents, only 16.4%, 14.1%, 7.0%, 16.4% and 10.2% followed a healthy dietary pattern of regular intake of breakfast, three square meals, milk, fruits and vegetables respectively. 50%, 38.3% and 45.3% followed an unhealthy dietary pattern of regular intake of sweets, chewing gum and soft drinks. With regards to body mass index and academic performance, less than 40% of the respondents were of normal weight and only half of the respondents had good academic performance. Body mass index, breakfast consumption, eating three square meals and regular intake of fruits and vegetables all had significant effects (P <0.05) on the academic performance of adolescents. Also, there was a significant joint effect of body mass index and healthy dietary pattern on the academic performance of these adolescents. Parents and school authorities should make all efforts to ensure healthy dietary pattern among adolescents so as to enhance their academic performance.