A 9-year-old neutered male rabbit (Oryctolagus cuniculus) previously diagnosed with right nephromegaly was presented with increased sexual behavior associated with hypertestosteronemia. Left adrenomegaly and an obstructive mass in the right renal pelvis and proximal ureter leading to severe hydronephrosis of the right kidney were diagnosed by abdominal ultrasound. A left adrenalectomy and right nephrectomy were performed and samples were submitted for histopathology, confirming the diagnosis of adrenocortical carcinoma and a transitional cell carcinoma of the ureter and renal pelvis. Increased sexual behavior resolved within 2 months following surgical resection of the affected left adrenal gland, but recurred 8 months later. The right adrenal gland had increased in size when compared to earlier ultrasonographic evalution. A 4.7-mg deslorelin implant was placed subcutaneously, which resulted in a decrease of testosteronemia and sexual behaviors for up to 18 months.