Renal abscesses are rare conditions in children, but they must be remembered in differential diagnosis of fever and abdominal pain. The authors report two paediatric cases with unusual presentation. Case 1: a 15-year-old girl was admitted following a period of fever, vomiting and left hypochondrium pain which became more localised to the left lower ribs. Blood tests suggested bacterial infection, but urinalysis and culture were negative. Renal CT scan presented features of bilateral pyelonephritis and left renal abscesses, while ultrasound remained normal until the ninth day of disease. Case 2: a 2-year-old girl, with diagnosis of β-thalassemia minor, had intermittent diffuse abdominal pain with 2 weeks of evolution. Renal ultrasonography and CT scan showed a heterogeneous mass compatible with Willms tumour. Intraoperative diagnosis was compatible with renal abscess with isolation of Proteus mirabilis in the fluid. Both responded well to long-term antibiotics and to surgical drainage (in the second case).