Estimates based on questionnaire responses are presented of the percentage and number of women who used selected substances during their lifetime and in specific time periods over the 12 months preceding delivery. The report also examines patterns of substance use by race/ethnic group, age, and other characteristics of the mother, and trends in the rates of use over the past year. In addition, estimates made from tests of urine specimens for illicit drugs are compared with rates of recent drug use based on self-reports. The following are some of the key findings from the report: (1) An estimated 5.5 percent, or 221,000 women, used an illicit drug at least once during pregnancy; (2) Marijuana was used by 2.9 percent, cocaine by 1.1 percent, and a psychotherapeutic medication without physician orders by 1.5 percent; and (3) Overall and within race/ethnic groups, rates of use during pregnancy of marijuana, cocaine, and cigarettes often were significantly higher for women who were not married, currently not employed, had less than 16 years of formal education, or relied on public aid for payment of the hospital. Figures, tables, exhibits, appendixes