Background and Objectives: This study aimed to determine the accuracy of a diet quality measurement tool, the Total Diet Score (TDS) using two validation methods; firstly the TDS calculated from a food frequency questionnaire (FFQ) was compared to the TDS calculated from weighed food records (WFRs); secondly the TDS was compared to a number of dietary biomarkers. Methods and Study Design: Data were collected from a population based cohort study located in the Blue Mountains region of Sydney, Australia. To compare dietary assessment tools, a sub sample of 75 subjects (aged 63 to 83 years) completed the FFQ and three, four-day WFRs at baseline. Fasting blood samples were collected from 2897 subjects at the first follow up in 1997-1999. TDS scores were calculated from both WFRs and FFQs. Methods to compare FFQ TDS scores to WFR TDS scores included paired t-tests, Pearson correlations, Bland-Altman plots, joint classification quartiles and weighted kappa scores. Linear regression analyses were used to assess the relationship between TDS and biomarkers. Results: No significant mean difference was found between FFQ TDS and WFRs TDS (p=0.63) with a significant positive correlation seen between the two methods (r=0.75, p<0001). The Bland-Altman method found no linear trend between the differences and means of TDS scores between the FFQ and WFR (p=0.38). A significant trend for higher serum vitamin B-12, serum folate, homocysteine and lower total cholesterol was found with increasing TDS. Conclusions: These findings suggest that the TDS is a useful tool for assessing diet quality in an older population.