OBJECTIVE: To evaluate the effectiveness of hypnosis to convert a breech presentation to a vertex presentation. DESIGN: Prospective case series compared with historical, matched comparison group. SUBJECTS: One hundred pregnant women whose fetuses were in breech position at 37 to 40 weeks' gestation and a matched comparison group of women with similar obstetrical and sociodemographic parameters derived from databases for other studies from the same time period and geographical areas. INTERVENTION: The intervention group received hypnosis with suggestions for general relaxation with release of fear and anxiety. While in the hypnotic state women were asked for the reasons why their baby was in the breech presentation. As much hypnosis was provided as was convenient and possible for the women until they were delivered of the baby or the baby converted to the vertex position. MAIN OUTCOME VARIABLES: A successful conversion for the intervention group was scored when the baby spontaneously converted to the vertex position before delivery or successful external cephalic version. The conversion rate of the intervention group was compared with the comparison group who received standard obstetrical care without the opportunity for hypnosis. DATA ANALYSIS: Parametric testing of statistically significant differences in the rate of conversion between the two groups. RESULTS: Eighty-one percent of the fetuses in the intervention group converted to vertex presentation compared with 48% of those in the comparison group. This difference was statistically significant. CONCLUSIONS: Motivated subjects can be influenced by a skilled hypnotherapist in such a manner that their fetuses have a higher incidence of conversion from breech to vertex presentation. Psychophysiological factors may influence the breech presentation and may explain this increased frequency of conversion to vertex presentation.