We provided CDC recommended postpartum tetanus, diphtheria, acellular pertussis (Tdap) immunization to medically underserved, uninsured women in Houston through a standing order protocol. From January 7-April 30, 2008, 1129 of 1570 (72%) postpartum women (93% Hispanic; 11% < or = 19 years) received Tdap before hospital discharge. Tdap uptake was 96.2% in women without self-reported contraindications. Recall of immunization history was inaccurate in 32% of unimmunized women who reported receiving antepartum immunization. Black women refused Tdap more often than other ethnicities (24% versus 8%; P=0.003). Postpartum Tdap immunization was successfully implemented in a high-risk population through a standing order protocol. Barriers to postpartum immunization include inaccurate immunization history and the need for ongoing targeted education.