Because the small backs of young children offer little space for atopy patch testing, it would be helpful to use smaller chambers. We therefore compared 6-mm chambers with the 12-mm chambers used in previous studies. We performed 55 double-blind, placebo-controlled food challenges in 30 children (17 boys, 13 girls) aged 3 to 58 months (median, 13 months). Sensitivity, specificity, positive predictive value, negative predictive value, and efficiency results show that the 12-mm chamber size yields much better results than the 6-mm chamber size. Therefore, 12-mm cups should be used for atopy patch tests with food, even in infants and small children.