Various tumors secrete tumor-specific substances capable of producing signs and symptoms in host organs not caused by direct tumor invasion or organ destruction. These symptoms are collectively referred to as "remote effects" or "paraneoplastic syndromes" of malignancy. Paraneoplastic syndromes are uncommon in childhood cancer. In Wilms tumor several distinct paraneoplastic syndromes have been reported: hypertension, erythrocytosis, hypercalcemia, Cushing syndrome, and acquired Von Willebrand disease. In addition some tumor-specific substances are known to be elevated in patients with a malignancy without causing specific symptoms. These so called "tumor markers" can be used to detect early recurrence in previously treated patients, or in the evaluation of patients undergoing adjuvant therapy. Five of particular interest are erythropoietin, neuron-specific enolase (NSE), hyaluronic acid (HA), hyaluronic acid-stimulating activity (HSA), and hyaluronidase.