Giant bladder calculi are common in adults but rare in children. In paediatric population,predisposing factors differ and typically include urinary stasis, congenital anomalies of the kidney and urinary tract, infections, dehydration and malnutrition. Metabolic abnormalities often under-diagnosed. A 3-year-old girl, from non-consanguineous marriage with nosignificant family history , presented with 2-day history of acute abdominal pain and oliguria. She experienced recurrent, self-limiting episodes over preceding year. Her pain score ranged 2- 6/10, haemodynamically stable, afebrile, with suprapubic tenderness. Baseline investigations, including inflammatory markers were normal. Urinalysis showed presence ofleucoerythrocytes and positive nitrite, though no positive culture. Radiography revealed large bladder calculi and right kidney calculus. Antibiotic commenced for presumed urinary tract infection with nephrolithiasis and referred to paediatric surgery and urology . Two bladder stones successfully removed during vesicolithotripsy . Inborn error of metabolism screening was non-diagnostic. However, urinary cystine was markedly elevated (669.02 mmol/mol creatinine; normal