Brain autopsy materials from 2 patients with myotonic dystrophy (MyD) were studied. The results obtained in these 2 cases were quite similar. Besides thalamic inclusion bodies and minor abnormalities in gyral architecture with a disordered cortical cellular arrangement, some new observations have been made. First, no more than one intracytoplasmic inclusion body per cell was present in the cerebral cortex, the thalamus, the caudate nucleus and the putamen; this inclusion body was oval or elongated with smooth, sharply defined contours and was usually located at the periphery of the cell. Second, irregular intracytoplasmic inclusion bodies, often multiple and not surrounded by a halo, were found at the periphery or within accumulations of neuromelanin granules in the pigmented cells of the substantia nigra. All the bodies described above stained highly eosinophilic with hematoxylin-eosin and the ultrastructure of the bodies in the thalamus and the substantia nigra was almost the same; these bodies were composed of stacks of alternating parallel, light and dark rectilinear profiles oriented perpendicularly to the longitudinal axis of the bodies. Third, Marinesco bodies were observed with a very high frequency in the pigmented cells of the substantia nigra.