Although shellfish allergy frequently results in emergency department visits, national prevalence studies focusing on shellfish allergy in children are scarce. This study describes parent reports of shellfish allergy among children in the United States. Data from shellfish-allergic children were identified for analysis from a randomized, cross-sectional survey administered in US households with children from June 2009 to February 2010. Child characteristics, parent-reported prevalence, severity, symptoms, diagnostic methods, and reaction history were analyzed as weighted proportions. Adjusted models were estimated to examine the association of child characteristics, reaction history, and diagnosis methods with odds of shellfish allergy and severe shellfish allergy. Among the 38,480 children included in this study, 499 were reported to have a shellfish allergy, corresponding to a prevalence of 1.3%. The mean age for first reaction to shellfish allergy was 5.8 years. Nearly one-half of all children with shellfish allergy had a history of severe life-threatening reactions (47.1%). Shellfish allergy was diagnosed by a physician at a rate of 58.5% (35.0% confirmed with testing), significantly lower than the rate of diagnosis for other common childhood food allergies (72.7%). Children with a shellfish allergy had lower odds (odds ratio, 0.39; 95% CI, 0.28-0.54) of developing tolerance compared with children with other common food allergies. Childhood shellfish allergy is a serious and underdiagnosed problem in the United States. Findings suggest that the impact of disease may be greater than previously reported. Accordingly, efforts are needed to improve awareness and management of shellfish allergy among children in the United States.