Data from a 20-year longitudinal study of 125 males and 126 females born to Black teenage mothers in a Baltimore hospital between 1966 and 1968 were analyzed to identify early childhood, middle childhood, and early adolescence determinants of functional literacy. All 251 subjects were interviewed in 1987, and 202 of them completed a document literacy questionnaire. The questionnaire responses were subjected to a multivariate regression analysis. Demographic data and data from preschool cognitive and behavioral assessments and interviewer evaluations of the subjects' households/household members at different times throughout the study were also collected. Preschool cognitive and behavioral functioning was found to be highly predictive of literacy in young adulthood even when the effects of family environmental characteristics such as living arrangements, quality of home environment, maternal education, and income are controlled. Grade failure in elementary school was linked to later literacy; however, the effect of grade failure disappeared when the measure of preschool abilities was controlled. Family environmental factors identified as being predictive of literacy were as follows: maternal education, family size in early childhood, maternal marital status, and income in middle childhood and early adolescence. (Appended are data tables. Contains 61 references.) (MN)