Antineutrophil cytoplasmic antibodies (ANCA) have been identified in a wide variety of vasculitic disorders, but it is controversial whether ANCA are present in the sera of patients with HSP. This prospective study was designed to assess the place of ANCA, particularly their IgA subclass, in HSP. Thirty-five patients (18 boys, 17 girls) aged 9.4+/-4 (3-16) years with a clinical diagnosis of HSP based on American College of Rheumatology (ACR) criteria were enrolled. Thirteen patients (6 boys, 7 girls) aged 8.3+/-5.5 (2-21) years with other vasculitides, consisting of classic polyarteritis nodosa (PAN) (n=2); cutaneous polyarteritis nodosa (n=1); acute infantile hemorrhagic edema (n=2); acute urticarial vasculitis (n=2); hypocomplementemic vasculitis (n=1); and unclassified vasculitis (n=5) served as disease controls and 10 healthy children served as normal controls. Twenty-five HSP patients and 7 disease controls were re-evaluated in the resolution phase that was described as 4-6 weeks after all symptoms subsided and all medications were stopped. Blood samples for ANCA and IgA rheumatoid factor (RF) were studied by indirect immunofluorescence (IIF) and ELISA, respectively. IgG ANCA was significantly lower in percentage in HSP patients (2.8%) than in disease controls (40%) (p=0.002). In contrast, IgA ANCA in cytoplasmic pattern was detected in a significantly higher percentage of HSP patients (82.3%) in the acute phase compared to those in the disease controls (38%) (p=0.004). In the resolution phase, IgA ANCA was negative in 88% of the patients (p= 0.001 for acute vs resolution phases). Neither IgG nor IgA ANCA were seen in normal controls. No relationship was found between disease severity of HSP and IgA ANCA. Positive IgA rheumatoid factor was present in only two patients with HSP. In conclusion, our results suggest that IgA ANCA may be useful to confirm the diagnosis of HSP in children.