Many parents of food allergic children have concerns about the development of food allergies in their other children.We sought to determine prevalence of food sensitization and clinical food allergy among siblings of food allergic children.Two thousand eight hundred and thirty-four children were enrolled in the Chicago Family Cohort Food Allergy study. One thousand one hundred and twenty children (ages 0-21 years) with a food allergy (defined by a reported reaction history and evidence of food-specific IgE or skin prick test) and at least 1 biological sibling were included in this study.Among siblings of children with food allergy, 33.4% had no sensitization and no clinical symptoms to food. Fifty-three percent had a positive food serum-specific IgE or skin prick test, but no reported symptoms of food allergy. Only 13.6% of siblings were both sensitized and clinically reactive to the same food. Milk allergy was the most common allergy among siblings (5.9%), followed by egg allergy (4.4%) and peanut allergy (3.7%).In a large cohort of food allergic families, only a small proportion of siblings were both sensitized and clinically reactive to a food. Sensitization without reactivity was common among siblings. Testing for food allergy in siblings without a history of clinical reactivity appears to be unjustified. Screening may lead to negative consequences related to potential misdiagnosis and unnecessary avoidance of a food. More data are needed to determine the absolute risk of food allergy development in siblings of food allergic children.