Five episodes of micropsia, which were precipitated by oedipal masturbatory fantasies, are described in the analysis of an adult male. Traumatic visual events and testicular retractions during the oedipal and latency years predisposed the ego functions concerned with visual perception to later involvement in conflict. The micropsia itself is seen as defending against castration anxiety by means of a series of unconscious fantasies of denial. These fantasies cause a regression to an earlier mode of visual perception (and to micropsia) characteristic of latency. The defensive modifications of the functions of the ego itself seen in micropsia are closely allied to those seen in the dèjá vu experience and in depersonalization.