The diet quality index (DQI) for preschool children is a new index developed to reflect compliance with four main food-based dietary guidelines for preschool children in Flanders. The present study investigates: (1) the validity of this index by comparing DQI scores for preschool children with nutrient intakes, both of which were derived from 3d estimated diet records; (2) the reproducibility of the DQI for preschoolers based on a parentally reported forty-seven-item FFQ DQI, which was repeated after 5 weeks; (3) the relative validity of the FFQ DQI with 3d record DQI scores as reference. The study sample included 510 and 58 preschoolers (2-5-6.5 years) for validity and reproducibility analyses, respectively. Increasing 3d record DQI scores were associated with decreasing consumption of added sugars, and increasing intakes of fibre, water, Ca and many micronutrients. Mean FFQ DQI test-retest scores were not significantly different: 72 (so 11) v. 71 (Si) 10) (P-=0-218) out of a maximum of 100. Mean 3d record DQI score (66 (so 10)) was significantly lower than mean FFQ DQI (71 (so 10); P<0.001). The reproducibility correlation was 0.88. Pearsons correlation (adjusted for within-person variability) between FFQ and 3d record DQI scores was 0.82. Cross-classification analysis of the FFQ and 3d record DQI classified 60% of the subjects in the same category and 3% in extreme tertiles. Cross-classification of repeated administrations classified 62% of the subjects in the same category and 3% in extreme categories. The FFQ-based DQI approach compared well with the 3d record approach, and it can be used to determine diet quality among preschoolers.