The anatomic and etiologic diagnosis of paralysis of the oculomotor, trochlear and abducens nerves is usually not difficult. A thorough knowledge of the course, and especially of the relationships, of the three nerves and of the predilections of certain infectious, toxic, vascular and neoplastic processes for these structures helps in clinical orientation. Frequently these nerves are implicated by diseases and injuries of the structures with which they are anatomically related, and a knowledge of the anatomic and pathologic pictures of, and the clinical manifestations produced by, the implicated structures is indispensable for the diagnosis of palsy of the extraocular muscles. The most common causes of paralysis of the extraocular muscles still remain syphilis, vascular lesions, diabetes, neoplastic processes, acute suppurative and nonsuppurative infections of the nervous system, chronic degenerative processes, exogenous intoxications, mushroom poisoning, botulism and myasthenia gravis. A diagnosis of some of these diseases is possible after a single