We report the uncommon clinical course of a female with right-sided hemi-hyperplasia. At the age of 2 years and 2 months, a small spherical lesion of the right kidney was detected by ultrasound and magnetic resonance tomography. When the patient was 4 years and 7 months, the very slowly growing tumor was removed completely and diagnosed as intermediate risk stage I nephroblastoma. The case demonstrates that even small renal lesions require diagnostic work-up and adequate treatment.