There are some pathological conditions which, though of considerable interest to the student of morbid anatomy, appear to have very little importance from the point of view of clinical study. The reason for this, sometimes at least, lies in the fact that it is difficult, if not impossible, to diagnose the onset and follow the progress of the morbid process during the life of the patient. Pachymeningitis interna hemorrhagica is essentially a condition of this kind. It is a morbid state which has been named and described for years, and yet it is a condition the diagnosis of which during life is extremely difficult. As a rule, when it is demonstrated at the post mortem, the clinical records of the case furnish us with no definite information suggestive of its presence. Often when symptoms point to the likelihood of its presence no lesion is found, while it occurs in cases which during life showed nothing special to indicate the possibility of such a condition.