The purpose of this study was to determine the effects of unilateral posterior mobilization and unilateral anterior mobilization of the sacroiliac joint (SIJ) on the standing position of the pelvis. Noninvasive methods were used to measure the position of the pelvis of 20 healthy men before and after SIJ mobilization. Ten subjects received posterior mobilization and 10 subjects received anterior mobilization. Two test sessions were conducted to check measurement reliability, followed by mobilization and a third test session. Apparent leg lengths were also measured before and after mobilization. Reliability was fair to high for the measurements. ANOVA for repeated measures revealed significant differences (p < 0.05) among the three tests for two measurements; however, post hoc analysis showed no significant differences between the measurements before and after mobilization. Mobilization had no effect on leg lengths. The benefits of SIJ mobilization should be considered in spite of these nonsignificant results because a small sample size of healthy men was examined, and because small changes in SIJ relationships may be sufficient to relieve low back pain.J Orthop Sports Phys Ther 1988;10(3):77-84.