This cross-sectional study aims to explore the dietary patterns and associated factors of adolescents, which are often overlooked in nutrition data systems. Face-to-face interviews were conducted with 304 participants aged 10 to 19 in rural northern Thailand, utilizing both open recall and list-based 24 h recall techniques, with the data recorded online. Dietary diversity (DD) was assessed using ten food groups as per the Food and Agricultural Organization guidelines. We employed binary logistic regression and multivariable logistic regression analyses. Most participants consumed items from the grains, white roots, and tubers food group, while the nuts, seeds, and pulses food group was the least consumed. The mean number of food groups consumed was 5.23 ± 0.12, with no significant differences across gender and age groups, and participants reporting no influence of mass media on food choices were more likely to have inadequate DD (AOR = 2.94; 95% CI 1.38-6.28). Conversely, those not influenced by social media when choosing food (AOR = 0.45; 95% CI 0.21-0.96), who felt relaxed during meals (AOR = 0.33; 95% CI 0.19-0.59), and with no role in family meal decisions (AOR = 0.55; 95% CI 0.31-0.95) were less likely to have inadequate dietary diversity. We suggest that assisting adolescents with mealtime management and involving them in selecting healthy menus could improve their dietary variety. Moreover, future research should further investigate these mechanisms to inform strategies for improving DD in this age group.