This paper explores personalization and depersonalization with special emphasis on the ego function of self-constancy. We regard the self as an intrapsychic structure and the ego as a group of functions that differentiates and integrates the self and, amongst many other things, maintains an affective experience of 'me-ness'. Defects in self-object differentiation, in self-constancy and in object constancy result in psychotic, borderline and narcissistic vulnerabilities to depersonalization. Sudden changes in the self representations not conforming to the average expectable self challenge self-constancy and may result in depersonalization. Depersonalization may at times be a signal affect denoting challenge to self-constancy from ego fixation or regression or from the presence of previously unavailable self- or self-object representations. It may in another model, at times, be a defensive affect protecting the ego from painful stimuli arising within the self-structure.