This report describes some additional morphologic observations on a mediastinal ganglioneuroma. The neoplastic neurons contained argentaffin cytoplasmic granules presumably representing neurosecretory granules. Cytoplasmic inclusions resembling Pick's bodies were frequently observed in the neuronal components of the tumor. These inclusions consisted of neurofilaments mixed with a variable number of microtubules, dense core vesicles and other organelles. These findings expand the range of conditions in which Pick's bodies are found.