Examined in this document is the effect the age at which a young woman has her first birth has on her later childbearing. Data from the Michigan Panel Study of Income Dynamics and the National Longitudinal Survey of Young Women are used in conjunction with a review of related literature in examining such factors as fertility, premarital pregnancy, religious background, educational achievement, family background, labor force status, race, birth cohort, age, and social class, and their roles in affecting subsequent family size. Findings presented indicate that the initiation of parenthood during the teen years seems to be associated with considerably larger families later in life. In addition, it is pointed out that given the high cost of rearing children to adulthood, teenage mothers face heavy economic demands over a long period of time, potentially contributing to poverty and/or welfare recipiency. (Author/EB)