Objective: To evaluate diets in terms of nutritional characteristics and quality from the perspectives of health, greenhouse gas emissions (GHGEs) and possible associations with each other in a representative sample of students at a public university. Design: Cross-sectional. Dietary intake was evaluated with a validated food frequency questionnaire, and diet quality was assessed through the Healthy Eating Index (HEI-2010) and MedDietScore (MDS). GHGE data were obtained from the literature. In addition, sex, socioeconomic status (SES) and body fat (BF) status were analysed as covariates. Setting: Basque Autonomous Community, Spain. Participants: 26,165 healthy adults aged 18-28 years. Results: Student diets were characterised by low consumption of carbohydrates (38·72% of total energy intake (TEI)) and a high intake of lipids (39·08% of TEI). Over half of the participants had low dietary quality. The low-emitting diets were more likely to be consumed by subjects with low HEI-2010 scores (β: 0·039 kg eCO2/1000 kcal per day) and high MDS scores (β: −0·023 kg eCO2/1000 kcal per day), after controlling for sex, SES and BF status. Both the low-emitting and healthy diets were more likely to be consumed by women and by those with normal BF percentage. Conclusions: UPV/EHU university students’ diets were characterised by moderate quality from a nutritional perspective and moderate variation in the size of carbon footprints. In this population, diets of the highest quality were not always those with the lowest diet-related GHGEs; this relationship depended in part on the constructs and scoring criteria of diet quality indices used.