PURPOSE: To identify the necessity of more reasonable diagnostic criteria and the possibility of early prediction of coronary involvement in the higher risk group, we investigated and compared clinical and laboratory findings in the acute phase and coronary involvements in those younger (n=17) and older(n=53) than one year of age in Kawasaki disease(KD). METHODS: Retrospective chart reviews were performed on 70 patients with KD who were admitted to the Chung-Ang University Hospital from April 1997 to May 2001. RESULTS: Male were significantly higher in the younger age group(M : F ratio 3.3 : 1 vs. 1.0 : 1, P=0.004). Fever durations before intravenous immunoglobulin(IVIG) and echocardiography were significantly shorter in the younger group(4.6+/-1.3 vs. 6.2+/-2.5, P=0.004 vs. 0.01, respectively). Cases meeting typical diagnostic criteria were significantly less in the younger group(P=0.006). In the laboratory findings, serum albumin, BUN and K+ levels in the acute febrile phase were significantly higher in the younger group(P=0.002, 0.006, <0.001, respectively) and incidences of coronary artery dilatation in the acute phase were significantly higher in the younger group(P=0.01). CONCLUSION: Although less met the typical diagnostic criteria of KD, infants younger than one year of age are more susceptible to coronary artery change in the acute febrile phase. Therefore, KD should be entertained as a diagnostic possibility in young infants with prolonged fever without distinct fever focus, and echocardiography should be considered as part of the evaluation of these patients, and then early diagnosis and prompt IVIG should be conducted.