We describe a 3 1/2-year-old boy with the Klippel-Trenaunay and Sturge-Weber syndromes. The child had congenital superficial capillary hemangiomas, congenital glaucoma and mild hydrocephalus. During the first year of life he experienced intermittent hematuria. When he was 3 years old he presented with seizures and left hemihypertrophy first was noted. Several months later radiological examination of a large abdominal mass demonstrated its origin to be in the right kidney. Radical nephrectomy documented the presence of renal hemangioma with complicating perirenal hematoma. A double inferior vena cava was another unexpected surgical finding that complicated the course of this patient. All of these unusual features in these rare syndromes with their clinical, pathogenetic and therapeutic implications are discussed. The differential diagnosis of renal masses in these syndromes also is presented.