Striatonigral degeneration. A clinicopathological study. The clinical and pathological features of 10 cases of striatonigral degeneration are described: 5 were misdiagnosed in life as Parkinson's disease. Retrospectively, helpful early pointers to the diagnosis in these cases included unexplained falls, autonomic dysfunction, absence of rest tremor and failure to respond to L-dopa, but these were not always present. The pathological diagnosis could not be excluded on macroscopic examination of the striatum. Relative preservation of the putamen occurred in the 4 patients who benefited from L-dopa. The caudate nucleus was involved in all cases and there was no sparing of the large striatal neurons. In mild cases, involvement of the putamen was confined to its posterior two-thirds, dorsolaterally. With increasing severity this extended in a dorsal to ventral and posterior to anterior direction. Seven of the cases had evidence of olivopontocerebellar damage, but only 2 of these had clinical evidence of cerebellar disease. Correlation was found between the neuronal counts in caudate:putamen, striatum:nigra compacta, globus pallidus:nigra compacta, nigra compacta:locus coeruleus. The most severely involved part of the substantia nigra pars compacta was the ventrolateral zone, which projects to the dorsal putamen, the earliest site of striatal disease. 