and at completion of the study. A 2-head gamma camera equipped with LEHR collimators was used for data acquisition (128 x 128 matrix, pixel size 3 mm, 128 projections, 360° circular orbit). FBP with a Butterworth prefilter (0.55 cycles/cm, order 10) was used for reconstruction, applying uniform attenuation correction. Voxel-based SPM approach was used for SPECT analysis using a paired t-test to compare baseline and post-treatment data. Results: A clear-cut cognitive improvement was observed in PDD pts after 6-month treatment with ChEIs (p< 0.01 for the total ADAS.cog score). While the total MMSE score increased slightly but nonsignificantly at 6 months, the MMSE subscores improved significantly (p<0.01), deteriorating again upon drug withdrawal. No difference in motor performance (UPDRS) was observed. Sequential SPECT analyzed by SPM showed a significant rCBF increase (p < 0.01) in several clusters within anterior cingulated and frontal regions bilaterally after ChEIs vs baseline, without any associated reduction in rCBF. No difference in the pattern of changes of rCBF was observed between PDD pts treated with rivastigmine and those treated with donepezil. Conclusion: Chronic treatment with ChEIs produced in PDD a striking improvement in cognitive mainly prefrontal functions, without worsening of parkinsonian features. These findings confirm the pivotal role played by the cholinergic system in dementia associated with PD. The increase of frontal perfusion after ChEIs treatment might suggest that the clinical improvement is associated with a sort of re-afferentation in the caudate-cortical connecting systems.