Mesoblastic nephroma is a rare renal tumour mainly observed in neonates and young infants. The authors report a case in a 5-day-old new-born infant presenting with an isolated abdominal mass occupying the left hypochondrium and flank. Ultrasonography demonstrated a 4 cm heterogeneous mass in the lower pole and middle of the left kidney. CT showed an intensely contrast-enhanced heterogeneous mass. The patient was treated by left radical nephrectomy with an uneventful postoperative course. The outcome was favourable without recurrence with a follow-up of one year. Mesoblastic nephroma is considered to be a benign tumour. The diagnosis is suggested by clinical, ultrasonographic and CT findings. Treatment is based on radical nephrectomy. In the light of this case, the authors discuss the clinical, radiological and therapeutic aspects of this tumour.