Former studies suggest an additional involvement of the sensory nervous system, beside the involuntary contractions of antagonist muscles, in idiopathic hand dystonia. We studied contact heat-evoked potentials and quantitative sensory testing (QST) in 10 patients suffering from idiopathic hand dystonia and 10 age-matched healthy controls. Cortical potentials recorded from the vertex (Pz) after contact heat stimulation of the volar forearm and the dorsum of the hand at a temperature of 51°C showed significantly reduced A-δ-amplitudes. Numerical pain ratings on the affected side in comparison to the unaffected side and to healthy controls were significantly reduced. QST results showed an impairment of the thermal detection thresholds, the mechanical pain sensitivity and the mechanical pain threshold at the affected body side of the patients. Our results suggest a loss of distinct sensory functions of the affected hand in comparison with the contralateral hand and to matched healthy subjects in patients suffering from idiopathic hand dystonia. For the first time, an extended loss of sensory function could be shown in patients suffering from idiopathic hand dystonia. © 2010 Movement Disorder Society.