Aim: The diagnosis of Kawasaki disease (KD) in those outside the typical age range (6 months-4 years) is often delayed, potentially worsening prognosis. The features of KD in children <= 6 months and >= 5 years were compared with those presenting within the more typical age distribution.Methods: Korean children with complete diagnostic criteria for KD were grouped according to their age at presentation: Group A (<= 6 months), Group B (7 months-4 years) and Group C (>= 5 years). The clinical features, laboratory findings and outcome in each group were compared.Results: Of 136 children presenting to a single centre between 1999 and 2003, 10 children were in Group A, 114 in Group B and 12 in Group C. The mean total fever duration was 8 days in Group C and 6.2 days in Group A (P = 0.03). All children in Group C had cervical lymphadenopathy, compared with 50% of Group A and 64% of Group B (P = 0.01). Coronary artery lesions were commoner in older children (Group C, 42%) compared with Group B (17%, P = 0.05). All children had an equivalent leukocytosis, but Group C had significantly higher neutrophil counts (P = 0.001). Group A had significantly lower mean haemoglobin (P = 0.003) and total protein (P = 0.002) at presentation and a more marked thrombocytosis 1 week after intravenous immunoglobulin therapy (P < 0.05).Conclusion: The clinical and laboratory phenotype of KD varies with age. Older children may have a more marked inflammatory response and worse outcome. Younger children who are treated appropriately may not have a chance to higher risk of coronary artery lesions.