Background: Sensitivity to the bitter compound 6-n-propylthiouracil (PROP) is genetically mediated. Sensitivity to PROP has been associated with weight status in both adults and children. Objective: To determine whether there is an association between PROP sensitivity and BMI in low-income children of diverse race/ethnicity, among whom there is a high prevalence of obesity. Methods and Procedures: Eighty-one preschool-aged children attending Head Start tasted a solution of 560 μmol/l PROP and reported whether it tasted "like water" or "like something else". Mothers reported child's race, age, maternal education, maternal weight and height, child's reluctance to sample new foods via the Food Neophobia Scale (FNS), and child's dietary intake using a food frequency questionnaire. Child weight and height were measured. BMI was calculated and for children, expressed in z-scores. Regression analyses were used to evaluate the relationship between child's PROP taster status and BMI z-score, testing covariates child's age, gender, race, maternal education and BMI, and child's FNS score. Children's dietary intake was compared by PROP taster status. Results: PROP tasters, compared with nontasters, had significantly higher BMI z-scores (0.99 (s.d. 1.24) vs. 0.03 (1.12), P = 0.004) and had a significantly higher prevalence of overweight (31.8% vs. 5.6%, P = 0.025), but demonstrated no differences in reported dietary intake. The most parsimonious model predicting the child's BMI z-score included only maternal BMI and the child's PROP taster status (R 2 = 22.3%). Discussion: A genetically mediated ability to taste bitter may contribute to obesity risk in low-income, preschool-aged children.