We evaluated sensorimotor processing in patients with writer9s cramp using PET and H215O blood flow scans. The study included six right-handed patients with unilateral writer9s cramp and eight right-handed normals. Subjects had blood flow scans at rest and during vibration of either the “affected” or “unaffected” hand. Vibration produced a consistent peak response in primary sensorimotor area (PSA) and supplementary motor area (SMA), both contralateral to the vibrated hand. Both responses were significantly reduced approximately 25% in patients with writer9s cramp (PSA, p = 0.002; SMA, p = 0.02) whether vibrating the affected or unaffected hand. This indicates that patients with unilateral writer9s cramp have bilateral brain dysfunction. These data provide objective evidence of abnormal central sensorimotor processing in writer9s cramp.