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Sacral nerve stimulation has proven to be a promising treatment for fecal incontinence when conventional treatment modalities have failed. There have been several hypotheses concerning the mode of action of sacral nerve stimulation, but the mechanism is still unclear. This study was designed to evaluate the results of rectal volume tolerability, rectal pressure-volume curves, and anal pressures before and six months after permanent sacral nerve stimulation and to investigate the mode of action of sacral nerve stimulation.Twenty-nine patients with incontinence (male/female ratio = 6/23; median age, 58 (range, 29-79) years) underwent implantation of a permanent sacral electrode and neurostimulator after a positive percutaneous nerve evaluation test. Wexner incontinence score, rectal distention with thresholds for “first sensation,” “desire to defecate,” and “maximal tolerable volume,” rectal pressure-volume curves, anal resting pressure, and maximum squeeze pressure were evaluated at baseline and at six months follow-up.Median Wexner incontinence score decreased from 16 (range, 6-20) to 4 (range, 0-12;P< 0. 0001). Median “first sensation” increased from 43 (range, 16-230) ml to 62 (range, 4-186) ml (P= 0.1), median “desire to defecate” from 70 (range, 30-443) ml to 98 (range, 30-327) ml (P= 0.011), and median “maximal tolerable volume” from 130 (range, 68-667) ml to 166 (range, 74-578) ml (P= 0.031). Rectal pressure-volume curves showed a significant increase in rectal capacity (P< 0.0001). The anal resting pressure increased significantly from 31 (range, 0-109) cm H2O to 38 (range, 0-111) cm H2O (P= 0.045). No significant increase in maximum squeeze pressure was observed.For patients with fecal incontinence successfully treated with sacral nerve stimulation, there was a significant increase in rectal volume tolerability and rectal capacity. A significant increase in anal resting pressure, but not in maximum squeeze pressure, was found. We suggest that sacral nerve stimulation causes neuromodulation at spinal level.