After an introduction and historical sketch of this rare and interesting disease, the authors give a detailed analysis of the recorded fifty-seven cases as to aetiology, symptomatology, prognosis, diagnosis, and treatment. The aetiology rests largely upon a family predisposition of degeneration, plus a transient and slight excitant of the character of a toxic or autotoxic agent In the development of the disease epilepsy appears first a few weeks to several years in one half the cases; in rare cases the epilepsy ceases in later life. The epileptic attacks are usually grand mal in character, preceded by myoclonic spasms. For a greater or longer period of time after the fits the patient is free from his myoclonus. The myoclonus is often atypical in degree and character. There is usually much mental impairment attending the development and end of the disease. The prognosis is poor, yet life is often prolonged for years, the patient dying finally of inanition, pulmonary congestion, and premature senility. The children begotten of myoclonic epileptics usually die early of an intercurrent affection, yet they in turn may live to develop the disease. The disease has been found in many cases indirectly as well as directly transmissible. The disease is largely one of the family type of neurosis. The authors place emphasis upon the fact that faulty diagnosis is the result of laying too much stress on single symptoms of the disease. The treatment, while largely palliative, must be undertaken with great care in the proper use of large doses of sedatives. Bromides rank in first place. The hypochlorisation adjuvant principle is highly recommended. Cases not benefited by bromides are decidedly in the minority. Chloral in connection with bromides is recommended in stubborn cases. Care of the diet, general hygiene, and a non-stimulative country existence are found to give best results. The authors present three new cases, which, in addition to one previously reported by Clark, constitute the only cases of the association disease at present in the English language. A study of the cortex in one case under ideal conditions of methods was made, and lesions found were in the second and third layer of cells, those of sensory and motor type. The changes in the second or sensory type are those which the authors have previously urged as the characteristic lesion of epilepsy, while those in the third or large pyramid cell are charged to the myoclonus. The lesions as demonstrated by camera lucida drawings were a destruction of the intra-nuclear network and its replacement by a granular substance. As a consequence of this change in the cell, body abstraction of the nucleolus occurred easily and frequently in making the sections. The exhaustive lesion of chromatolysis was shown over the entire cortex. The pathogenesis of the association disease appears to be an intoxication or auto-intoxication of motor and sensory cortical cells, probably brought about by a faulty chemotaxis of such because of their inherent cellular anomaly.