To study the effects of Florida's 1989 expansion in the Medicaid income eligibility threshold for pregnant women, the authors performed concurrent and longitudinal comparisons with matched birth and death certificates, hospital discharge data, Medicaid eligibility records, and records from county health departments for women giving birth in a 12-month period in 1998-1989 or in calendar year 1991. Measures included the amount and timing of prenatal care and rates of low birthweight and infant death. Medicaid expansion led to greater access and improved birth outcomes. For example, the rate of low-birthweight infants among low-income women without private insurance fell from 69.7 to 61.8 per 1000, while it remained unchanged for low-income women with private insurance. Women in the expansion group who used county health departments had fewer low-birthweight infants than those using other delivery systems. The benefits from the Florida expansion appear to be greater than those reported for others states. The role of the public health delivery system may account for some of Florida's success.