College of Medicine, Yonsei University, Seoul, Korea Wilms tumor is the second most common malignant retroperitoneal tumor. Inferior vena cava and right atrial involvement is found in about 4-10% and 0.5-3% of cases, respectively. But, right ventricular involvement has not been reported. We experienced a case of Wilms tumor with right ventricular invasion in a 2 year-old male who presented intermittent hematuria and abdominal pain. Computed tomogram and echocardiogram showed a homogeneous mass extended to right ventricle via inferior vena cava. He received pre-operative chemotherapy followed by operation, radiation therapy including heart, and post-operative chemotherapy.