Estimates of diet-disease relative risks (RRs) suffer from inaccuracies introduced by dietary measurement errors. Using the "method of triads," by which the validity coefficient (VC) of the dietary assessment method and "true" long-term intake could be estimated from 3 pairwise correlations between the FFQ, the reference method, and the biomarker, the authors evaluated the performance of a newly developed FFQ. Over a period of 13 mo (September 2000 to September 2001), 161 participants completed 3 FFQs and six 24-h recalls (24HRs), and supplied 2 blood samples and three 24-h urine collections. For protein, beta-carotene, and folic acid, the VCs of the FFQ with the "true intake" (0.77, 0.65, and 0.72, respectively) were relatively higher than the VCs of 24HRs (0.68, 0.60 and 0.39, respectively). Among the biomarkers, the VCs of serum beta-carotene and folic acid with the "true intake" (0.65 and 0.65) were higher than the VCs of urinary nitrogen and alpha-tocopherol (0.44 and 0.34, respectively). The DEARR study showed that the newly developed FFQ is a valid and reproducible instrument for assessing dietary intake. The VCs obtained can be used for future adjustment of diet-disease RR estimates in this population.