Accumulation of α‐synuclein has been associated with neurodegenerative disorders, such as Lewy body disease and multiple system atrophy. We previously showed that expression of wild‐type human α‐synuclein in transgenic mice results in motor and dopaminergic deficits associated with inclusion formation. To determine whether different levels of human α‐synuclein expression from distinct promoters might result in neuropathology mimicking other synucleopathies, we compared patterns of human α‐synuclein accumulation in the brains of transgenic mice expressing this molecule from the murine Thy‐1 and platelet‐derived growth factor (PDGF) promoters. In murine Thy‐1‐human α‐synuclein transgenic mice, this protein accumulated in synapses and neurons throughout the brain, including the thalamus, basal ganglia, substantia nigra, and brainstem. Expression of human α‐synuclein from the PDGF promoter resulted in accumulation in synapses of the neocortex, limbic system, and olfactory regions as well as formation of inclusion bodies in neurons in deeper layers of the neocortex. Furthermore, one of the intermediate expresser lines (line M) displayed human α‐synuclein expression in glial cells mimicking some features of multiple system atrophy. These results show a more widespread accumulation of human α‐synuclein in transgenic mouse brains. Taken together, these studies support the contention that human α‐synuclein expression in transgenic mice might mimic some neuropathological alterations observed in Lewy body disease and other synucleopathies, such as multiple system atrophy. © 2002 Wiley‐Liss, Inc.