Patterns of dopaminergic cell loss in the midbrain and patterns of mesostriatal fiber loss in the caudate nucleus and putamen are described for cases of idiopathic Parkinson's disease. Neither cell loss nor fiber loss is homogeneous. In the midbrain, quantitative analysis points to a selective vulnerability of neurons in the most heavily pigmented dopaminergic cell groups. In the striatum, a dorsolateral-to-ventromedial gradient of loss appears to characterize both the caudate nucleus and the putamen. These patterns of loss and sparing have implications both for analysis of the clinical symptoms of Parkinson's disease and for study of the etiology of this disease.