Haemolytic Uremic Syndrome (HUS) is a thrombotic microangiopathy frequently triggered by Shiga toxin-producing E. coli (STEC). This report compares two paediatric cases caused by the same pathogen (E. coli O157:H7) with divergent clinical outcomes. In the first case, early hyperhydration and azitromycin treatment prevented renal failure. Conversely, the second patient developed severe acute kidney injury requiring intensive care and dialysis due to inadequate initial fluid replacement. These cases show that timely and aggressive hyperhydration is a critical intervention that can significantly alter the disease course and prevent permanent organ damage