The frequency and degree of stiatopallidonigral (SPN) degeneration were examined in 41 autopsy cases of Pick's disease. Based on the degree of SPN degeneration, these cases were arranged into four groups: 1) group I (severely degenerate; 19.5%), 2) group II (moderately degenerate; 22.0%), 3) group III (mildly degenerate; 36.5%), and 4) group IV (non-degenerate; 22.0%). 17 of the 41 cases had a definite (moderate to severe) SPN degeneration. The striatum, especially the caudate nucleus, was most frequently and most severely affected, while the internal segment of the globus pallidus was least frequently and least severely affected. In general, the oral portions of the SPN nuclei were more severely involved. In addition, in the putamen and globus pallidus the dorsomedial portions adjacent to the internal capsule were apt to be affected more markedly than the other portions. In the substantia nigra the degeneration tended to be more predominant in the pars reticulata than in the pars compacta, although both were usually involved. In addition, the medial to central portions of the substantia nigra were more vulnerable. In comparing the severely and moderately degenerate groups (groups I and II) with the mildly and non degenerate groups (groups III and IV), the former had more female cases, longer duration of illness, and more third-stage cases. In addition, the former contained more cases with lower brain weight and (predominant) frontal atrophy type, and more atypical cases without Pick bodies, or with symmetrical pyramidal tract degeneration or with combined traumatic lesions. It is notable that in all cases with definite SPN degeneration no extrapyramidal involuntary movements had been detected.