Fecal incontinence at night may be a disturbing consequence of ileal pouch-anal anastomosis (IPAA). The hypothesis was that decreases in anal canal resting pressure occur as sleep deepens and that the decreases are more profound in pouch patients with incontinence than in controls. Using a sleeve catheter assembly for recording intraluminal and canal pressure and polysomnographic recordings of sleep stages, progressive decreases in anal canal resting pressure with deepening sleep occurred in 11 healthy controls (mean +/- SEM: 57 +/- 3 mm Hg to 43 +/- 3 mm Hg: P less than 0.05) and in 11 patients after IPAA (55 +/- 3 mm Hg to 42 +/- 4 mm Hg; P less than 0.05). Minute-to-minute variations in mean pressure were also found in both controls and IPAA patients, and they were greater at night in patients (P less than 0.05), except during rapid eye movement (REM) sleep. In three patients, resting pressure during REM sleep decreased markedly to 31 +/- 8 mm Hg. This decrease plus the variations in pressure during REM sleep led to incontinence. In conclusion, decreases in anal resting pressure coupled with marked minute-to-minute variations in pressure during sleep occurred in controls and in patients after IPAA and, when profound, led to nocturnal fecal incontinence in some patients.