In a patient with symptomatic liver metastases of a neuroendocrine tumor larger than 10 cm in diameter percutaneous radiofrequency ablation was performed. The ablation resulted in a significant decrease in tumor size and a good long-term improvement of symptoms. Plasma serotonin 48 hours after the ablation was approximately 10-fold lower than before. However, sequential determination of plasma serotonin during the radiofrequency ablation revealed a two-fold increase of plasma serotonin induced by the procedure. There was also an approximately three-fold increase of 5-hydroxyindol acetic acid in urine in the 24 hours following the ablation. The data show that ablation procedures in neuroendocrine tumors may induce hormone release which may be critical in patients with severe clinical symptoms.