A 23-year-old woman was referred to our hospital with persistent hypertension over 5 years irrespective of medication. Her blood pressure on admission was 210/130 mm HG. She had no family history of hypertension. Biochemical evaluation revealed hypo-potassium (2.7 mEq/L) and a high concentration of plasma rennin activity (20.6 ng/mL/h). An abdominal computed tomography scan showed 1-cm iso-density, and a weak contrast-enhancing solid mass in the right kidney cortex (Fig. 1a). Magnetic resonance imaging (MRI) with and without gadolinium showed a well-defined iso-intensity mass in the right kidney by T1 weighted image. The mass showed lowintensity in fat saturation T2-weighted image with weak contrast-enhancement, and high-intensity in diffusion magnetic resonance imaging (MRI) (Fig. 1b). This MRI finding was suggestive of reninoma. Although selective venous sampling failed to show any significant difference in the rennin activity between the right and left renal vein, it was highly suspected that this kidney tumor was producing rennin. After the patient’s written informed consent was obtained, the right kidney tumor was removed by laparoscopic partial nephrectomy. The tumor was well-capsulated and its cutting surface was white. Histological and immunohistochemical examinations revealed that the tumor had inconspicuous nuclear morphism and plenty of rennin granules in the cytoplasm (Fig. 1c). Two hours after tumor removal, the concentrations of plasma rennin and aldosterone were normalized. A few days after the operation, the patient’s blood pressure had been normalized. Reninoma should be considered when hypertension is uncontrollable with hypo-potassium. As far as we know, only 89 cases of reninoma have been reported. This is the third patient who was successfully treated with laparoscopic partial nephrectomy.