Background/Aims: Assessing secular trends of diet quality at the population scale is an important tool for health policymakers. The aim of this study was to describe secular trends in energy intake and diet quality in a representative Mediterranean population, accounting for energy underreporting. Methods: We analyzed the dietary data from 4,061 men and 4,409 women who were included in 2 population-based cross-sectional studies conducted in northeast Spain in 2000 and 2005. The surveys included randomly selected free-living men and women between 35 to 74 years of age. Results: No significant differences in reported energy intake between 2000 and 2005 were observed. Protein (p = 0.014) and carbohydrate (p = 0.02) consumption (expressed as percent of total energy intake) decreased in men and women, respectively. Energy density and intake of total, saturated and monounsaturated fat were significantly higher (p < 0.001) in 2005 than in 2000 in both genders. In contrast, lower consumption of fibre, fruit and meat (p < 0.001) was observed for both genders in 2005 compared to 2000. A significantly lower proportion of men and women met the recommended intake for carbohydrates, total fat, saturated fat, cholesterol and fruits in 2005 when compared to 2000. When energy underreporters were excluded from the analysis, a decline in energy intake (p < 0.001) and an increase in fish consumption (p < 0.001) between 2000 and 2005 was observed in men; no other significant differences were found in diet quality and food consumption trends among non-underreporters. Conclusions: Whereas energy intake remained stable from 2000 to 2005, overall diet quality showed an unfavourable trend during this timeframe. Secular dietary trends did not change their magnitude or direction, with the exception of energy and fish consumption in men, after excluding energy underreporters from the analysis.