Self-concept is known to affect motivation to change substance use behaviors, and may be particularly salient during pregnancy. To isolate psychological processes specific to pregnancy from psychological processes associated with the transition to parenthood, we examined a sample of birth mothers who made postnatal adoption placements. We hypothesized that self-concept as a provider would be related to cessation of tobacco, alcohol, and illicit drug use during pregnancy. We obtained lifetime and pregnancy substance use history and psychological measures at 3 to 4 months postpartum from 693 birth mothers using Life History Calendar and computer-assisted personal interviewing methods. Using logistic regression, we assessed the association of self-concept as an adequate provider with cessation of substance use during pregnancy, controlling for sociodemographic variables, depressive symptoms experienced during pregnancy, past year antisocial behaviors, familial substance abuse, timing of pregnancy recognition, and timing of initiation of prenatal care. More positive self-concept as an adequate provider was independently associated with cessation of substance use and earlier initiation of prenatal care during pregnancy. Familial substance abuse, depressive symptoms, and antisocial behaviors during pregnancy were inversely related to cessation. Maternal substance use during pregnancy is a common modifiable risk factor for poor birth outcomes, and is associated with long term psychological risks to offspring. Enhancing maternal identity as a provider for the fetus during pregnancy, along with treatment of depression, may improve motivation to stop substance use.