Objective: To examine diet- and body size-related attitudes and behaviors associated with supplement use in a representative sample of fourth-grade students in Texas. Design: Cross-sectional data from the School Physical Activity and Nutrition study, a probability-based sample of schoolchildren. Children completed a questionnaire that assessed supplement use, food choices, diet-related attitudes, and physical activity; height and weight were measured. Setting: School classrooms. Participants: Representative sample of fourth-grade students in Texas (n = 5967; mean age = 9.7 years standard error of the mean [SEM] = 0.03 years, 46% Hispanic, 11% African-American). Main Outcome Measures: Previous day vitamin supplement consumption, diet- and body size-related attitudes, food choices, demographic factors, and physical activity. Analysis: Multivariable logistic regression models, P less than 0.05. Results: The prevalence of supplement use was 29%. Supplement intake was associated with physical activity. Girls who used supplements were more likely to report positive body image and greater interest in trying new food. Relative to nonusers, supplement users were less likely to perceive that they always ate healthful food, although supplement use was associated with more healthful food choices in boys and girls (P less than 0.001). Conclusions and Implications: The widespread use of supplements and clustering of supplement use with healthful diet and greater physical activity in fourth graders suggest that supplement use be closely investigated in studies of diet-disease precursor relations and lifestyle factors in children. (Contains 3 tables.)