PURPOSE: Intravenous immunoglobulin (IVIG) is effective for the treatment of idiopathic thrombocytopenic purpura (ITP) in children. Recently, several reports have been published that show its impact on the absolute neutrophil count. The present study was performed to confirm these findings. METHODS: Data on 26 ITP patients were analyzed. Patients with febrile illness or increased C-reactive protein levels at presentation, which would influence the neutrophil counts, were excluded to determine the sole impact of IVIG. In addition, patients who received steroid treatment were also excluded. RESULTS: Sixteen boys and ten girls were analyzed. For patients who received an IVIG dose of 0.4 g/kg/day (n=17), the absolute neutrophil count (ANC) measured next day was significantly decreased. For patients who received an IVIG dose of 1 g/kg/day (n=9), the ANC measured the next day was also significantly decreased. However, the decrease was more profound in the high-dose group compared to the low-dose group. Among six cases with profoundly decreased ANC greater than 1,000/ mm3, four patients (67%) received IVIG at a dose of 1 g/kg/day. All four cases with increased ANC were treated with IVIG dose of 0.4 g/kg/day, and three cases (75%) among them had a febrile reaction during IVIG administration. None of the cases with decreased ANC had a febrile reaction. No cases had infectious complications reported. CONCLUSION: IVIG treatment for ITP patients appears to suppress the ANC. This decrease of ANC was more pronounced when a higher dose of IVIG was used. Some cases with increased ANC counts after IVIG use were found only in low-dose IVIG group, and was associated with febrile reactions during IVIG use.