We present an adolescent boy with unilateral supernumerary breast. It was a V type by Leung Clasification. Despite the average occurence between 0.22% and 6% in a normal population we have not had other cases in the last 20 years. The patient was an asthenic boy of sixteen in the IV stage of puberty. Sometimes he felt swelling and tenderness in this breast tissue two years ago. These symptoms became worse two months ago. At the admission he was symptom free. In the right hypochondrium inferomedially he had a nipple and areola with a small part of the glandular tissue. The axilla was empty. After an excision we got a 15 x 10 x 8 mm specimen. Pathohistological report described incompletely formed mammary lobule with smooth muscles and lactiferous ducts of nipple in dermis. This was consistent with the diagnosis of ectopic breast tissue. He wanted it removed for esthetic reasons. His hormonal state was normal. All blood checks were normal. Kidney ultrasound was normal. His grandmother had pyelon duplex and frequent uroinfections. As it is known, there is an association between supernumerary breast tissue and renal malformations. Since he did not have it, we think that a routine screening of the uropoetic system should be performed in any patient with supernumerary breast.