While the incidence of back pain during pregnancy has been shown to be high, few studies have investigated postural changes that occur during pregnancy and their relationship to back pain. The purpose of this study was to determine if posture and back pain changed from the first to the third trimester of pregnancy and whether there was a relationship between the two. Twelve healthy women who were having uncomplicated pregnancies participated in the study. During the first and third trimesters, each subject had their standing posture and back pain assessed by a Metrecom Skeletal Analysis System and a 0- to 10-cm line pain scale, respectively. Repeated measures analysis of variance and Pearson correlation coefficients were calculated on or between back pain and nine posture variables and revealed significant increases in third trimester back pain and postures compared with first trimester back pain (p < .05) and postures for lumbar angle (p < .01), posterior head position (p < .01), right pelvic sagittal tilt (p < .01), and left pelvic sagittal tilt (p < .01). No significant relationships were found between magnitude of or change in posture and back pain. These results suggest that in the standing position the lumbar lordosis and sagittal pelvic tilt increased and head position become more posterior as women progressed from the first trimester to the last trimester of pregnancy. These postural changes, however, were not related to back pain. This suggests that many of the posture-correcting clinical exercise regimens given to pregnant women need to be investigated.