A healthy 5-year-old boy was brought to the Emergency Department with a 24-hour-history of fever, abdominal pain, bloody diarrhoea and vomiting. Blood tests and ultrasound of the abdomen suggested an acute gastroenteritis. The boy was admitted and intravenous fluids were started. Twenty-four hours later macrohaematuria, oliguria, anaemia, thrombocytopoenia and increased serum creatinine levels were observed. Due to the rapid onset of acute renal failure, Haemolytic Uremic Syndrome (HUS) was suspected and the child was transferred to a Paediatric Nephrology Unit where blood transfusions and dialysis were performed, with gradual recovery of his renal function. The presence of Shiga-like-Toxin-producing Escherichia coli (STEC) on the stool samples confirmed the diagnosis. An early diagnosis of HUS is important in order to treat complications promptly.