OBJECTIVES To document the patterns of first-order fertility rates associated with extreme maternal ages in Taiwan; determine if there is a gap in adverse birth outcomes (specifically low birth weight and prematurity) between adolescent mothers and older mothers; and determine which factors are important in explaining the differences in adverse birth outcomes between adolescent mothers and older mothers. STUDY DESIGN Government statistics and survey data [Taiwan Birth Cohort Survey (TBCS)]. METHODS Descriptive statistics and logistic regression. RESULTS Between 1989 and 2009, the first-order fertility rate for mothers aged 15-19 years decreased, whereas that for mothers aged 35-49 years increased. Analysis of TBCS data revealed that, in comparison with older mothers, adolescent mothers are not necessarily at higher risk for adverse birth outcomes. Birth complications, pregnancy-related risks, adequate number of prenatal care visits and weight gain are more important than socio-economic status and prevalence of smoking in determining birth outcomes among first-time mothers of extreme reproductive ages. Adolescent mothers are less likely to have birth complications and pregnancy-related risks, but are more likely to have an inadequate number of prenatal care visits and to gain an inadequate amount of weight compared with older mothers. CONCLUSIONS The risks associated with adolescent mothers are easier to manage than the risks associated with older mothers. Their birth outcomes can be improved through good policy. Taiwan's health policy should target specific risks to reduce the number of adverse birth outcomes among adolescent mothers rather than try to prevent all childbearing during adolescence.