Objectives: The aim of this work was to study the prevalence and significance of antineutrophil cytoplasmic autoantibodies in sera of patients with acute post-streptococcal glomerulonephritis. Methods: We investigated 41 children with acute post-streptococcal glomerulonephritis (APSGN) and 13 children with acute streptococcal infection (without nephritis) in addition to 15 healthy age and sex matched controls for the presence of antineutrophil cytoplasmic antibodies (ANCA) to elaborate their pathophysiologic role in APSGN. Results: ANCA were detected only in sera of 5 children (12%) of APSGN patients, three of them (60%) showed atypical cytoplasmic pattern “C-ANCA" and two (40%) showed perinuclear pattern “P-ANCA".On the other hand ANCA were not detected in children with acute streptococcal infection or the controls. We found that hypertension, blood urea, serum creatinine, proteinuria and haematuria were significantly higher in ANCA positive than in ANCA negative APSGN patients. On follow up after one month, the ANCA positive APSGN patients showed the same titer of these autoantibodies and did not show a significant improvement of renal function tests in contrast to the ANCA negative APSGN children. Conclusions: The positive correlation found in our study between the level of ANCA titer and the disturbed renal function tests pointed to the possible role of these autoantibodies in the pathogenesis of APSGN and the disease progression. The absence of ANCA in the acute streptococcal infection suggested that their presence is not just an epiphenomenon of the heterogenous humoral immune response due to the streptococcal infection. We concluded that ANCA testing in children with APSGN could predict those with an unfortunate outcome and orientate the clinicians to focus their efforts in prevailing chronic renal damage.