Background Eating habits are developed during the preschool years and track into adulthood, but few studies have quantified dietary quality of meals packed by parents for preschool children enrolled in early care and education centers. Objective Our aim was to evaluate the dietary quality of preschoolers' sack lunches using the Healthy Eating Index (HEI) 2010 to provide parents of preschool children with guidance to increase the healthfulness of their child's lunch. Design This study is a cross-sectional analysis of baseline dietary data from the Lunch Is in the Bag trial. Participants A total of 607 parent-child dyads from 30 early care and education centers in Central and South Texas were included. Main outcome measures Total and component scores of the HEI were computed using data obtained from direct observations of packed lunches and of children's consumption. Statistical analysis Three-level regression models with random intercepts at the early care and education center and child level were used; all models were adjusted for child sex, age, and body mass index (calculated as kg/[square meter]). Results Mean HEI-2010 total scores were 58 for lunches packed and 52 for lunches consumed, out of 100 possible points. Mean HEI component scores for packed and consumed lunches were lowest for greens and beans (6% and 8% of possible points), total vegetables (33% and 28%), seafood and plant proteins (33% and 29%), and whole grains (38% and 34%); and highest for empty calories (85% and 68% of possible points), total fruit (80% and 70%), whole fruit (79% and 64%), and total protein foods (76% and 69%). Conclusions Parents of preschool children pack lunches with low dietary quality that lack vegetables, plant proteins, and whole grains, as measured by the HEI. Education of parents and care providers in early care and education centers is vital to ensure that preschoolers receive high dietary-quality meals that promote their preference for and knowledge of a healthy diet. (author abstract)