We compared the obstetric guidelines published by the American College of Obstetrics And Gynecology (ACOG) and Royal Colleges of Obstetricians and Gynaecologists (RCOG). The references and the recommendations in the current practice bulletins (PBs) and green guidelines (GGs) were compared. As of December 2007, there were 42 PBs and 27 GGs. There were nine common obstetric topics between ACOG and RCOG. Each GG had almost twice as many recommendations as the corresponding PB (median 7 versus 15; p < 0.0001); 28% of ACOG's recommendations were confirmed by RCOG and 16% disagreed. Recommendations of the common obstetric guidelines by ACOG and RCOG were not comparable the majority of the time.