Objective: To examine the relationships between physical and social self-concepts, motivational interviewing (MI), and nutrition assessment skills with dimensions of counseling self-efficacy. Design: Cross-sectional survey. Setting: Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) clinics. Participants: Sixty-five WIC nutritionists. Main Outcome Measures: Counseling self-efficacy on topics related to physical activity and nutritional behaviors and in the presence of language and cultural differences. Analysis: Multiple linear regression. Results: Nutritionists' perception of their own MI skills was positively associated with their self-efficacy for counseling clients of a culture different than their own, when counseling about physical activity, and when counseling about nutrition behavior. Hispanic ethnicity and social self-concept were positively associated with counseling self-efficacy when culture differences were present. Physical self-concept was positively associated with self-efficacy related to physical activity topics. Nutrition assessment skill was negatively associated with self-efficacy for working with non-English-speaking clients. Conclusions and Implications: Development of MI skills and strategies to improve social and physical self-concept may increase WIC nutritionists' counseling self-efficacy, particularly when counseling clients from diverse backgrounds. (Contains 3 tables.)