This study examined the association between dietary habits and behavioural problems at school among adolescents in Norway. Participants in this study included 517 adolescents and 336 of their parents. Students attended schools in the south of Norway, where the study was conducted. In 2012, adolescents completed a food frequency questionnaire (FFQ) and a questionnaire regarding behavioural problems at school. Parents completed a questionnaire regarding socioeconomic status. All statistical analyses were carried out using SPSS. High intake of soda with sugar and frequent consumption of take-away food were significantly associated with increased behavioural problems at school in the adjusted analysis, while frequent consumption of fast food and frequent consumption of dinner (as opposed to skipping meals) were significantly associated with decreased odds of behavioural problems only in the crude analysis (i.e., unadjusted for age, BMI, and parental SES). The study shows an association between diet and behavioural problems at school, even when adjusting for parental SES. The study underlines the importance of a healthy diet in adolescence and the importance of promoting both cooking skills and nutritional knowledge among adolescents at school.