OBJECTIVE: The 2004 American Heart Association (AHA) statement included a clinical case definition and an algorithm for diagnosing and treating suspected incomplete Kawasaki disease (KD). We explored the performance of these recommendations in a multicenter series of US patients with KD with coronary artery aneurysms (CAAs). METHODS: We reviewed retrospectively records of patients with KD with CAAs at 4 US centers from 1981 to 2006. CAAs were defined on the basis of z scores of >3 or Japanese Ministry of Health and Welfare criteria. Our primary outcome was the proportion of patients presenting at illness day < or =21 who would have received intravenous immunoglobulin (IVIG) treatment by following the AHA guidelines at the time of their initial presentation to the clinical center. RESULTS: Of 195 patients who met entry criteria, 137 (70%) met the case definition and would have received IVIG treatment at presentation. Fifty-three patients (27%) had suspected incomplete KD and were eligible for algorithm application; all would have received IVIG treatment at presentation. Of the remaining 5 patients, 3 were excluded from the algorithm because of fever for <5 days at presentation and 2 because of <2 clinical criteria at >6 months of age. Two of these 5 patients would have entered the algorithm and received IVIG treatment after follow-up monitoring. Overall, application of the AHA algorithm would have referred > or =190 patients (97%) for IVIG treatment. CONCLUSIONS: Application of the 2004 AHA recommendations, compared with the classic criteria alone, improves the rate of IVIG treatment for patients with KD who develop CAAs. Future multicenter prospective studies are needed to assess the performance characteristics of the AHA algorithm in febrile children with incomplete criterion findings and to refine the algorithm further.