Adherence to the Dietary Guidelines for Americans (DGA) may involve higher diet costs. This study assessed the relation between two measures of food spending and diet quality among adult participants (N = 768) in the Seattle Obesity Study (SOS III). All participants completed socio-demographic and food expenditure surveys and the Fred Hutch food frequency questionnaire. Dietary intakes were joined with local supermarket prices to estimate individual-level diet costs. Healthy Eating Index (HEI- 2015) scores measured compliance with DGA. Multiple linear regressions using Generalized Estimating Equations with robust standard errors showed that lower food spending was associated with younger age, Hispanic ethnicity, and lower socioeconomic status. Even though higher HEI-2015 scores were associated with higher diet costs per 2000 kcal, much individual variability was observed. A positive curvilinear relationship was observed in adjusted models. At lower cost diets, a $100/month increase in cost (from $150 to $250) was associated with a 20.6% increase in HEI-2015. For higher levels of diet cost (from $350 to $450) there were diminishing returns (2.8% increase in HEI- 2015). These findings indicate that increases in food spending at the lower end of the range have the most potential to improve diet quality.Copyright © 2020 Elsevier Ltd. All rights reserved.