RESUMEN
High level of the CA 125 serum antigen is typically associated with ovarian malignancies. However the CA 125 antigen can also be found in association with inflammation or neoplasms of tissues other than ovaries, i.e. mesothelial cells, mullerian duct derivatives and gastroenteric tract. Therefore the marker is not specific for ovarian neoplasms. In childhood there is not a large experience about clinical meaning of high CA 125 serum levels. We report a case in a 14-year-old patient, female, affected by hydronephrosis. Our case confirms that high CA 125, especially in childhood, is not necessarily associated with ovarian or pelvic diseases. Moreover the review of literature suggests the opportunity to investigate CA 125 serum levels in children affected by hydronephrosis.