To investigate the factors directly and indirectly associated with a cariogenic diet among southern Brazilian adolescents. This cross-sectional study included 15-19-year-old students attending high schools in Santa Maria, southern Brazil. The participants completed a questionnaire on sociodemographic and behavioral variables. The Oral Health Impact Profile-14 was applied to collect data on oral health-related quality of life (OHRQoL). Clinical examination was used to assess the dental caries status (decayed, missing, and filled teeth index). A cariogenic diet was considered a latent variable measured by the self-perception of a healthy diet and the frequency of consumption of sugary foods and drinks. Structural equation modeling was used to analyze the direct and indirect pathways to a cariogenic diet. A total of 1197 adolescents were included. Low toothbrushing frequency (standardized coefficient (SC), 0.10; p < 0.05), cigarette smoking (SC, 0.15; p < 0.01), and alcoholic beverages (SC, 0.14; p < 0.01) were directly linked to a cariogenic diet, which, in turn, was directly linked to untreated dental caries (SC, 0.18; p < 0.01) and poor OHRQoL (SC, 0.16; p < 0.01). In addition, household income (via toothbrushing frequency) and age (via alcoholic beverages) were indirectly linked to a cariogenic diet. A cariogenic diet was consistently associated with a range of unhealthy behaviors during adolescence as well as poor household income. Health promotion strategies to restrict sugar consumption and encourage healthier lifestyles should be aware of the synergism observed among unhealthy behaviors during adolescence.