Objective: To determine differences in clinical characteristics, laboratory findings, and cardiac complications between patients with acute Kawasaki disease who received additional treatment for persistent or recurrent fever vs those who did not. Design: Nonconcurrent case series; medical record review. Setting: Tertiary care pediatric hospital. Patients: One hundred eighty-five consecutive patients diagnosed as having acute Kawasaki disease at The Hospital for Sick Children, Toronto, Ontario, from 1995 to 1997. Main Outcome Measure: Prevalence of cardiac complications. Results: Twenty-one patients (11%) received additional treatment with intravenous gamma globulin (IVGG) with or without intravenous methylprednisolone for persistent fever lasting for more than 48 hours or recurrent fever after initial treatment with IVGG. Patients who received additional treatment did not differ significantly from other patients regarding age, sex, race, or diagnostic criteria. Compared with the patients who did not receive additional therapy, the patients who received additional treatment had shorter median interval from fever onset to initial dose of IVGG (5 vs 6 days; P =.006) and longer total days of fever (9 vs 6 days; P [is less than] .001). Initial laboratory investigations did not differ significantly. On initial echocardiography, patients who received additional therapy were significantly more likely to have pericardial effusion (33% vs 15%; P=.04), ventricular dysfunction (14% vs 2%; P=.002), and coronary artery ectasia (76% vs 43%; P=.004) but not aneurysms (10% vs 5%; P=.47). At 12 months after diagnosis, there were no significant differences between the 2 groups regarding the prevalence of coronary artery ectasia or aneurysms. Conclusion: Patients receiving additional treatment for persistent or recurrent fever have similar demographic and clinical characteristics, greater initial cardiac involvement, and similar overall outcomes. Arch Pediatr Adolesc Med. 2000;154:694-699