To clarify the neurological function of the puborectalis muscle (PM) in child patients with soiling after ileal J-pouch-anal anastomosis (IPAA) for ulcerative colitis (UC), we examined the terminal motor latency in the sacral nerves that regulate the PM. Eight patients after IPAA for UC were studied (6 males and 2 females aged 11 to 13 years with a mean age of 12.8 years). All patients 6 months after IPAA showed soiling (group A) and these patients showed continence at 2 years after IPAA (group B). Group C serving as controls consisted of 16 subjects (10 males and 6 females aged 12 to 17 years with a mean age of 14.4 years). Left-and right-sided sacral nerve terminal motor latency (SNTML) tests were performed at 6 months and 2 years after IPAA in order to measure the latency of the response in the bilateral PM following magnetic stimulation of sacral nerve root segments 2 to 4 (S2-S4) of the spinal column overlying the cauda equina. The following results were obtained. (1) Right-sided SNTML: group A exhibited significant prolongation compared with groups B and C (P < 0.0001 and P < 0.0001, respectively). There was no significant difference between groups B and C (P = 0.2329). (2) Left-sided SNTML: group A exhibited significant prolongation compared with groups B and C (P = 0.0002 and P < 0.0001, respectively). There was no significant difference between groups B and C (P = 0.2315). Note that significant differences were not established between SNTML values measured on the right and left sides. Soiling in child patients 6 months after IPAA may be caused by damage to the bilateral sacral nerves during the operation. However, the damage to the sacral motor nerve improves within 2 years after IPAA.