The thalamus is assumed to be involved in the generation of Parkinsonian tremor. Ten patients with tremor-dominant idiopathic Parkinson's disease (IPD) and strictly unilateral resting tremor were investigated by cerebral high-resolution 3-dimensional magnetic resonance imaging (MRI). MRI data were analyzed by an observer-independent morphometric technique, voxel-based morphometry (VBM). For VBM, MRI data were automatically normalized and segmented, then gray matter volumes were analyzed on a voxel-by-voxel basis in comparison to an age-matched control group using Statistical Parametric Mapping (SPM99). Highly significant structural changes, i.e. locally increased gray matter concentrations (P<0.001), were found in the nucleus ventralis intermedius (VIM) of the thalamus contralateral to the tremor side and were significantly covariant with tremor amplitudes. On the one hand, these changes were localized in close vicinity to a thalamic focal hypermetabolism as revealed by a previous positron emission tomography study in unilateral Parkinsonian tremor patients. On the other hand, the localization of the focal structural changes in VIM corresponds with the generally accepted target area of tremor surgery in IPD.