Background: C3 glomerulonephropathy (C3G) is a rare complement-mediated glomerular disorder resulting from dysregulation of the alternative complement pathway , characterised by dominant C3 deposition on immunofluorescence microscopy . In paediatric populations, its heterogeneous clinical phenotype frequently overlaps with post-infectious glomerulonephritis (PIGN). Case presentation: We report an 11-year-old girl who initially presented at six years of age with facial oedema, ascites, macroscopic haematuria, and hypertension following a respiratory tract infection. Laboratory evaluation demonstrated markedly reduced serum C3 with normal C4 levels, elevated anti-streptolysin O titres, and preserved renal function. She was managed as PIGN with supportive therapy . After defaulting follow-up for four years, she re-presented at 10 years of age with recurrent gross haematuria, oedema, nephroticrange proteinuria, hypertension, and renal dysfunction. Renal biopsy revealed strong C3-dominant staining in the absence of significant immunoglobulin deposition, confirming the diagnosis of C3 glomerulonephropathy . Immunosuppressive therapy with corticosteroids and mycophenolate mofetil resulted in renal recovery to her baseline function. During follow-up, she experienced multiple relapses with progressive deterioration of renalfunction. A subsequent renal biopsy demonstrated crescentic glomerulonephritis, necessitating intravenous cyclophosphamide therapy . Her clinical course was complicated by hypertensive encephalopathy , pulmonary oedema, and severe sepsis requiring prolongedintensive care. Although partial renal recovery was achieved, persistent proteinuria and a reduced estimated glomerular filtration rate were consistent with chronic kidney disease stage 2. Conclusion: This case highlights the relapsing and progressive nature of paediatric C3G, the diagnostic challenges associated with PIGN-like initial presentations, and the critical importance of early diagnosis to mitigate progression to chronic kidney disease.