Thirty temporal bones were dissected under the operating microscope, and four whole temporal bone specimens were studied by light microscopy for evaluation of the lateral malleal space and Prussak's space. In all specimens Prussak's space showed a blind end toward the anterior pouch and communicated with the posterior pouch. Its roof consisted of the lateral malleal ligamental fold, which was always strongest in its anterior half and as a rule had a thin area in its posterior portion. In four ears there was a membrane defect connecting Prussak's space to the lateral malleal space. The latter did not contain additional folds and communicated freely with the upper attic. The pathways for spread of an acquired primary cholesteatoma from Prussak's space are outlined.