Inherent limitations on the feasibility of experimentation have made it difficult for investigators to formulate an adequate understanding of individuality as a psychological phenomenon. Recently, Fiske (1979) and Sontag (1971) have suggested that application of a longitudinal or developmental strategy might be of some use in remedying this difficulty. A longitudinal study of individuality was carried out through the use of three scored autobiographical data forms tuned to particular developmental periods. Between the ages of 18 and 30, 415 males and 358 females, participated in three assessments in which they responded to 281 life history of biodata items. Subsequently, the item data collected over this developmental period for each sex group were entered into separate principal component analyses, and scores on the resulting components formed the basis for a set of Ward and Hook subgroupings. The 15 male subgroups and the 17 female subgroups generated an 84 percent and 86 percent classification ratio for the two sex groups. Examination of the subgroups' differential characteristics and a number of subsidiary analyses indicated that the various male and female subgroups met the essential requirements for the formation of robust and powerful developmental typologies. A marked similarity to the types identified by Block (1971) was noted along with certain other conclusions which flowed from the types' differential characteristics. A series of eleven tables, which provide detailed data analyses, is appended. (Author/WAS)