The relationship between birth weight and maternal sociodemographic characteristics was examined in a sample from two teaching hospitals in eastern Taiwan. Using a structured questionnaire, we conducted face-to-face interviews with women at antenatal clinics between 1998 and 1999 in Hualien City. One year later, we took the outcome of pregnancy from medical records and birth certificates from the Public Health Bureau of Hualien County. Of the 1,128 single live births, 6.8% had low birth weight (LBW) using the World Health Organization cut-off of 2,500 g. LBW was more common in teenage (< 20 years), older (> 30 years), first-time, and unmarried mothers; those with basic/intermediate educational attainment; and residents of aboriginal districts. Teenage pregnancies were more likely than those in adults to be unplanned, and such mothers had smoking or alcohol-drinking behavior. Prevention of teenage pregnancy is crucial to lower LBW rates in eastern Taiwan. For adult mothers, basic or intermediate educational attainment, residence in an aboriginal district, and first-term pregnancy were significant factors associated with LBW, after adjustment for other psychosocial attributes, such as psychologic distress and poor family support. Thus, we should pay more attention when caring for pregnant women with such sociodemographic characteristics, and ensure that they have adequate prenatal care and can adopt a healthy lifestyle.