Objective: High consumption of energy-dense foods has been linked to high energy intakes and excess weight gain. This study tested the hypothesis that high energy density of the total diet is associated with lower diet costs. Design: Dietary intakes of 837 French adults, aged 18–76 years, were assessed using a dietary history method. Dietary energy density (MJ kg −1 ) was calculated by dividing total energy by the edible weight of foods consumed. Daily diet cost (€day −1 ) was estimated using mean national food prices for 57 food items. The relationship between dietary energy density and diet cost at each level of energy intake was examined in a regression model, adjusted for gender and age. Results: The more energy-dense refined grains, sweets and fats provided energy at a lower cost than did lean meats, vegetables and fruit. Within each quintile of energy intake, diets of lower energy density (MJ kg −1 ) were associated with higher diet costs (€day −1 ). Conclusion: In this observational study, energy-dense diets cost less whereas energy-dilute diets cost more, adjusting for energy intakes. The finding that energy-dilute diets are associated with higher diet costs has implications for dietary guidelines and current strategies for dietary change.