Uncaria tomentosa (UT), also known as cat's claw, isa Peruvian Rubiaceae species widely used in traditional medicine for the treatment of a wide range of health problems. There is no report about the use, safety, and efficacy of UT in neurological disorders. We describe reversible worsening of motor signs in a patient with Parkinson disease after oral intake of UT, and some possible explanations are discussed. © 2008 Lippincott Williams & Wilkins.