During adolescence, teens start making their own food choices. While health and nutrition are important, practical and social concerns are also influential. This study aims to determine factors that motivate the food choices of Irish teens (using Food Choice Questionnaire), using data from the National Teens' Food Survey II (N = 428, 50% male, 13-18 years), and to identify how these motivations relate to dietary intakes (4-day semi-weighed food diaries). Data analysis used PCA to determine the food choice motivation subscales, and correlation and comparative statistical tests (t-test, ANOVA). Eight motivating factors were identified for Irish teens: Sensory Appeal, Price & Availability, Health & Natural Content, Familiarity, Ease of Preparation, Mood, Weight Control, and Ethical Concerns. Health and practical aspects to food choice (Price, Availability, Ease of Preparation) are important for teens, but taste (Sensory Appeal) remains a key influence. Food choice motivations vary by sex and by age, BMI status and weight perception, where girls were more motivated by health, weight control, mood and ethical concerns, and older teens were more influenced by mood and ease of preparation. Both those classified as overweight and those who perceived they were overweight were motivated more by weight control and mood for their food choices, whereas those who perceived their weight to be correct placed more importance on health and natural content. Those motivated by weight control had lower energy and higher protein intakes, and those motivated by health and natural content had more health promoting behaviours, with higher physical activity, lower screen time, and higher protein intakes. Understanding the motivations of teens' food choice can help understand why they struggle to meet dietary recommendations, and help to develop more effective health promotion messages by capitalising on the key motivations in the population.