The major determinant of infant mortality in the United States is low birthweight (LBW). Health behaviors related to LBW are inadequate prenatal care, poor nutrition, smoking, and moderate to heavy alcohol use. Before interventions can be designed to assist women in modifying these health behaviors, more must be understood about their causes. The Health Belief Model (HBM) is a framework for analyzing beliefs that motivate health behaviors and is well established as a model for understanding health behavior decisions. The chief aim of this study was to develop an instrument to assess women's health beliefs during pregnancy. Questions for the instrument were generated around the four major constructs of the HBM: perceived susceptibility, seriousness, benefits, and barriers. Four focus group interviews, a literature review, and consultation with an HBM expert provided content for questions. The questionnaire was administered to a convenience sample of 127 women. The measurement models were tested using confirmatory factor analysis. Parsimony was achieved by reducing the original 106-item scale to 64 items. The final instrument provides support for the HBM but not for all of its discrete constructs.