Since the days of antiquity an extremely important part has been assigned to suppression of the menses in the production of mental disorders; but in the opinion of modern alienists, who are opposed to the old humoral pathology, no more is to be recognized in this connection than the ordinary menstrual stimulus, which, indeed, when the soil is already prepared, may furnish a causal determinant for an increase in the intensity of an already existing anomalous mental condition. Quite recently numerous cases have been published in which such an influence has been recognized as powerful. _Von Krafft-Ebing_ writes: “In isolated cases, as a sequel of sudden cessation of the menstrual flow, generally, due to a fright or to a chill, the development of insanity (usually acute mania) has been observed, and the suppression of menstruation has been regarded as the causal determinant. It is indeed conceivable that the connection between the two events is supplied by a collateral vicarious congestion of the brain. As a rule, however, the psychosis and the suppression of menstruation are the coeffects of the same cause, and are both of vasomotor origin.” _Mairet_ reports a case of violent mental disorder of a maniacal type, associated with chorea, occurring at puberty, the exciting cause of which, in a constitution hereditarily predisposed to insanity, he believed to be suppression of the menses. _Diamant_ had under observation a girl in whom, at the age of six years, menstruation ceased, having previously been regular since the age of two years; after the suppression of menstruation, violent epileptiform seizures set in, occurring at what should have been the menstrual periods. _Westphal_ described a case of infanticide committed in a state of melancholia at the proper menstrual period, the menses being suppressed. Menstrual psychoses are observed for the most part in comparatively young women; after the age of thirty-five they are uncommon. Among _von Krafft-Ebing’s_ cases there were: 4 patients between the ages of 15 and 20 years. 6 patients between the ages of 20 and 25 years. 2 patients between the ages of 25 and 30 years. 6 patients between the ages of 30 and 35 years. 2 patients above the age of 35 years. The same author insists that for the development of a menstrual psychosis a predisposition on the part of the brain must exist, either in the form of an inherited predisposition, or in the form of a primary mental disorder, or, finally, as the result of some special exciting cause, such as emotional disturbance, the abuse of alcohol, or bodily illness. Among 19 cases observed by _von Krafft-Ebing_ 12 were hereditarily predisposed. 4 had previously exhibited great nervousness during menstruation. 7 suffered from primary mental weakness.