Intracranial tumors arising within or involving the midbrain and pons are of infrequent occurrence and often may be differentiated as to their exact site owing to the important structures which, as a rule, are involved separately and in a characteristic way in this area. There are some instances, however, in which the objective manifestations are confused or at least do not give clear-cut evidence of an exact localization. Furthermore, they are frequently mistaken for cerebellar lesions. In an effort to shed more light on such doubtful cases, a study of the tumors in this region has been undertaken. It is realized that, at the present, interest in such differentiation is largely academic, but there are three points of possible therapeutic moment to be considered. First, the pathologic type of tumor concerned may give a definite response to roentgen-ray treatment, and a more exact prognosis can then be offered. Second, tumors