The author has investigated patients suffering from disorders of the pupillary reflexes and of the tendon reflexes of the lower limbs which come under the heading of tonic pupil. Forty-five patients were followed up over a period of 15 years. The tendon reflexes of the lower limbs were recorded graphically and showed a very characteristic retardation of the second phase of the patellar reflex. The aetiopathogenesis of Adie's syndrome is discussed. The pathogenesis of Adie's syndrome has so far not been definitely established. We have merely tried to point out a few of the features which permit its early diagnosis and have drawn attention to the basic problem of the pathogenesis of certain neuro-muscular disorders on the basis of secondary considerations involved in this uncommon syndrome.