Background Only a minority of infants are exclusively breastfed for the recommended 6 months postpartum. Breastfeeding self-efficacy is a mother's confidence in her ability to breastfeed and is highly predictive of breastfeeding behaviors. The Breastfeeding Self-Efficacy Scale-Short Form (BSES-SF) was developed among English-speaking mothers to measure breastfeeding self-efficacy. Objectives To translate the BSES-SF into Spanish and assess its psychometric properties. Design Methodological study. Setting One public hospital in Orihuela, Spain. Participants A convenience sample of 135 in-hospital breastfeeding women was recruited on their second day postpartum. Methods The BSES-SF was translated into Spanish using forward translation, back-translation and pilot testing. Internal consistency, construct validity and predictive validity were assessed. A battery of self-report questionnaires was administered on the second day postpartum including: a questionnaire on sociodemographic variables and breastfeeding status, the translated BSES-SF, the Spanish adaptation of the General Self-Efficacy Scale and the Stress Management Self-Efficacy Scale. Also, data on breastfeeding status at three weeks postpartum were collected by telephone interviews. Results The Cronbach's alpha coefficient for internal consistency was 0.92. The translated BSES-SF presented a unidimensional structure with factor loadings of >0.30. In addition, demographic response patterns and correlations with self-efficacy scales provided further evidence of construct validity. In-hospital BSES-SF scores significantly predicted exclusive breastfeeding at 3 weeks postpartum. Conclusions The results of this study indicate that the Spanish translation of the BSES-SF can be considered a valid and reliable measure of maternal breastfeeding self-efficacy in Spain.