OBJECTIVE: To study the relationships among prepregnancy body mass index (BMI), women’s target gestational weight gain, and provider weight gain advice. METHODS: Project WISH, the acronym for Women and Infants Starting Healthy, is a longitudinal cohort study of pregnant women in the San Francisco Bay area. We excluded subjects with preterm birth, multiple gestation, or maternal diabetes. RESULTS: Among overweight women (prepregnancy BMI 26.1-29.0), 24.1% reported a target weight gain above the Institute of Medicine (IOM) guidelines, compared with 4.3% of normal weight women (P .001). Among women with a low prepregnancy BMI ( 19.8), 51.2% reported a target weight gain below the guidelines, compared with 10.4% of normal weight women (P .001). These patterns persisted in a multivariate analysis. Latina ethnicity, lower maternal education, low prepregnancy BMI ( 19.8), lack of provider advice about weight gain, and provider advice to gain below guidelines were all independently associated with a target weight gain below IOM guidelines. Prepregnancy BMI more than 26, multiparity, lower age, and provider advice to gain above guidelines were all associated with a target gain above IOM guidelines. CONCLUSION: Women’s beliefs about the proper amount of weight gain and provider recommendations for weight gain vary significantly by maternal prepregnancy BMI. Many women report incorrect advice about gestational weight gain, and women with high or low prepregnancy BMI are more likely to have an incorrect target weight gain. New approaches to provider education are needed to implement the IOM guidelines for gestational weight gain.