It is doubtful that psychological theories have fully posed much less resolved the question of the extent of sex differences in personality development. In this connection Sarason et al. comment: No one to our knowledge has denied they [such sex differences] are pervasive, and yet the problem of degree of pervasiveness has not been critically examined despite its implications for theory, methodology, and the direction of future research (23, p. 260). A perusal of the journals shows that many studies, which include both male and female Ss in the sample, do not make provisions for sex differences in the hypotheses. Where sex differences are found they are, consequently, rationalized post facto. Moreover, often no statistical analysis of sex differences is performed, despite their importance in psychological processes. This paper presents a theoretical formulation which postulates basic sex differences in the nature of sex-role and parental identification, as well as basic differences in the process of achieving such identification. The developmental processes described are considered neither inevitable nor universal. If they are appropriate to the U. S. culture today, they may, nevertheless, be inappropriate for many other cultures and for a significantly altered U. S. culture of the future. This formulation refers to the typical pattern, although recognizing that a typical pattern, if not a myth, is at least an exception. Research findings considered relevant to this formulation are reviewed.