Previous interpretations have not adequately explained the presence of focal neurological signs, delirium, and a variety of highly specific disturbances of perception, language, and sensorium in the case of Anna O. Examination of the neurological details suggests that Anna suffered from complex partial seizures exacerbated by drug dependence, and that she developed conversion symptoms patterned after the preexisting organic pathology. Hysterical conversion symptoms that mimic ictal events are not uncommon in psychomotor epilepsy. Recent neuropsychiatric models of hysteria are remarkably similar to the hypnoid states theory Breuer formulated, based on his observation of Anna O. The hypothesis presented here does not conflict with previous psychodynamic interpretations. I submit that it was the development of a conversion disorder patterned on actual organic phenomena, which highlighted for Breuer and Freud the "psychical mechanism" of somatic symptoms, thus paving the way for the important psychodynamic discoveries for which the case is remembered.