We sought to study the impact of the 2004 American Heart Association guidelines on diagnosis and treatment of patients with Kawasaki disease (KD). We reviewed patient records from July 2000 to June 2002 (group 1) and July 2007 to June 2009 (group 2) at a tertiary children’s hospital. The proportion of patients with incomplete KD in group 2 (56 of 118 [47%]) was significantly higher than that in group 1 (20 of 85 [24%], p = 0.001). Median age (months) and interquartile ranges for group 1 was 26 (range 12.5–52) and for group 2 was 38.5 (range 18–63; p = 0.072). The number of patients diagnosed with KD having just 2 symptoms other than fever was significantly higher in group 2 (2.4 vs. 16.9%, p < 0.001). Erythrocyte sedimentation rate, albumin, and alanine aminotransferase levels were obtained in a significantly greater number of patients with KD after the guidelines were published. Thirty-two of the 203 patients studied had coronary artery (CA) involvement (15.8%), 4 of whom had CA aneurysms (2%) and 28 had CA ectasia only (13.8%). CA involvement was seen in 13 of 85 (15.3%) patients in group 1 and 19 of 118 (16.1%; p = 1) patients in group 2. After publication of the 2004 AHA guidelines, diagnoses of incomplete KD and laboratory use increased at our center; however, the rate of CA involvement remained stable. There also was a trend towards older age in children diagnosed with KD. Laboratory parameters and CA involvement between incomplete KD and classic KD were comparable.