Objective: To determine the effect of patient position on the mobility of the urethrovesical junction. Methods: Q-tip tests in the supine and standing positions were performed on forty-six consecutive female patients with a variety of urogynecologic complaints. Wilcoxon signed-rank test and McNemar test were used to compare urethral mobility in the supine and standing positions. Results: Both the maximum straining Q-tip angle and the difference between the resting and straining angles were significantly greater in the supine position than in the standing position (P < .01). Thirty-four subjects had a positive Q-tip test in the supine position (defined as a maximal straining angle of at least 30°), but only 24 (71%) of these women had a positive Q-tip test in the standing position. Conclusion: Patient position has a significant effect on mobility of the urethrovesical junction, in that the female urethra is more mobile in the supine than in the standing position. Because the selection of a surgical procedure for a woman with genuine stress incontinence depends in part on the presence or absence of urethral hypermobility, this observation has important implications for the evaluation of women with genuine stress incontinence.