|Purpose:Intersphincteric resection(ISR) is the ultimate sphincter-preserving operation for low rectal cancer. This study assessed the long-term results of ISR in terms of oncologic safety and level of maintenance of defecatory function.Method:Patients (n=203) with lower rectal cancer underwent curative ISR, categorized as total, subtotal or partial resection of the internal anal sphincter between 2001 and 2015. Sphincter function was evaluated using manometry and anorectal sensation was evaluated preoperatively and postoperatively at 3, 6, and 12 months. Defecatory function was assessed 1 year after surgery using the following criteria; frequency of bowel evacuation, Kirwan grade, Wexner's score and m-FIQL.Results:The 5-year overall survival rate (OS) according to TNM stage was 91% for stage I, 95% for Stage II, 79% for Stage IIIa and 76% for Stage IIIb. The 5-year disease free survival rate(DFS) was 79.4% and the 5-year cumulative local recurrence rate was 5.7%. The frequency of bowel evacuation was 3.9, the Wexner's score was 7.9, the Kirwan grade was 2.1 and the mFIQL was 25.2. Multivariate analysis using logistic regression revealed that HPZ, AMES and level of ISR were not significant independent risk factors for postoperative incontinence.Conclusions: The long-term results suggest that ISR is the optimal sphincter-preserving surgery for low rectal cancer. However, the postoperative functional result should be carefully considered before selecting ISR because it is difficult to accurately predetermine the risk for postoperative incontinence.