CLINICAL PRESENTATION A 9-year-old boy known to have tuberous sclerosis complex (TSC) presented with gross hematuria. Three years earlier, a screening kidney ultrasound showed a left simple renal cyst and bilateral increased echogenicity of the corticomedullary regions. The child had no history of trauma, bleeding tendency, or other urinary symptoms. He was not taking any medications. His medical history is notable for retinal phakomas, cardiac rhabdomyoma, subependymal giant cell astrocytomas, and seizure disorder, as well as learning disabilities. Despite a family history of TSC in the mother and an elder sibling, no family member had kidney disease. On examination, the patient was afebrile with normal pulse and blood pressure. Abdominal examination findings were unremarkable, with no organomegaly. Laboratory investigation results were within the normal ranges, with serum creatinine level of 0.38 mg/dL (corresponding to estimated glomerular filtration rate of 135 mL/min/1.73 m as calculated by the Schwartz equation). Hemoglobin level was 11.8 g/dL; platelet count, 321 310/mL, and international normalized ratio, 1. Urinalysis showed albumin (11) and 4 squamous epithelial cells per high-power field (HPF), 12 white blood cells/HPF, and .60 red blood cells/HPF. Abdominal ultrasound and computed tomographic scan were obtained (Fig 1), and a left total nephrectomy was performed (Fig 2).