Abstract A prehypnotic suggestion is a specific suggestion administered prior to the formal or informal induction of the hypnotic treatment, but which does not become effective until after induction of the trance. The trance is defined as the hypnotic state characterized by an inward turning of the mind concomitant with an enhancement of the creative imagination, in a setting of reduced attention to, appreciation of, and interaction with the details of the external reality. An effective prehypnotic suggestion is characterized by the same compulsive triad as an effective posthypnotic suggestion, namely compulsivity, amnesia of its source and rationalization if challenged. It thus conditions the nature and accomplishments during the subsequent trance in a manner analogous to the way in which a posthypnotic suggestion conditions the results of the hypnotic treatment during the subsequent waking state. Unless careful notes are taken of the seemingly informal conversation prior to the induction of the hypnotic treatment, the result of an inadvertent prehypnotic suggestion may be mistaken for an inherent effect of the trance state per se. In the case of patients suffering from stuttering, for example, upon the prehypnotic suggestion that the patient will speak normally as soon as the trance will have been induced, the patient will speak normally during the trance, without any further reinforcement of the suggestion after induction of the hypnotic state. A prehypnotic suggestion may remain latent for years, until it is activated by the inward turning of the mind and the resulting enhancement of the creative imagination characteristic of the trance. A case report is presented illustrating this fact in the treatment of a chronic depression of psychasthenic-anhedonic type. This case also illustrates the fact that the prehypnotic suggestion need not to have been administered by the same therapist. Prehypnotic suggestions play a role in the structuring of different types of trances, such as those useful for anesthesia and pain relief for which distractions in the form of fantasy and hallucinatory experiences are useful, as compared to the highly personalized introspective trances useful for psychotherapy. Certain apparently spontaneous trance phenomena, as those described by Charcot in his report of his rediscovery of hypnosis, may also be attributable to prehypnotic suggestive influences.