The clinical recognition of a case of acoustic neuroma as a rule presents no special difficulties. The well established syndrome with progression of symptoms which follow a definite chronology, together with the usually typical objective neurologic observations, was vividly and accurately brought out by Cushing1 in his monograph on this subject in 1916. There are, however, some cases of verified acoustic tumors in which the history or neurologic signs do not conform entirely to the rule, and there are other cases of tumor in this general neighborhood giving symptoms so nearly like those of acoustic tumors as to cause confusion and error in diagnosis. Certain tumors of the pons fall into the latter group, and in looking up the records it appears that not infrequently these patients have been subjected to a suboccipital exploration which nearly always would have been inadvisable if a correct preoperative diagnosis had been made.