Substance use during pregnancy is a major public health concern. This study examined differences in substance use among pregnant women from rural and urban areas. Participants were 114 pregnant women entering a hospital-based inpatient detoxification unit primarily for Opiate Dependence who voluntarily agreed to a face-to-face interview. Substance use measures were based on the Addiction Severity Index gathering information about lifetime, past 12 months, and 30 days prior to admission. Rural pregnant women had higher rates of illicit opiate use, illicit sedative/benzodiazepine use, and injection drug use (IDU) in the 30 days prior to admission. Additionally, a greater proportion of rural pregnant women reported the use of multiple illegal/illicit substances in the 30 days prior to entering detoxification. More specifically, pregnant women from rural areas were 8.4 times more likely to report illicit opiate use, 5.9 times more likely to report IDU, 3.3 times more likely to report illicit sedative/benzodiazepine use, and 2.8 times more likely to report the use of multiple illegal/illicit substances in the 30 days prior to entering inpatient detoxification, after adjustment for socio-demographic characteristics (including education and income), pregnancy characteristics, physical and mental health indicators, and criminal justice system involvement. The increased rates of prescription opiate and benzodiazepine use as well as IDU among rural pregnant women are concerning. In order to begin to understand the elevated rates of substance abuse among rural pregnant women, substance use must be considered within the context of demographic, geographic, social, and economic conditions of the region.