AIM: To investigate the relationship between body mass index (BMI) and clinical outcomes after laparoscopic intersphincteric resection (Lap-ISR) for ultralow rectal cancer.METHODS:All consecutive patients treated by Lap-ISR for ultralow rectal cancer between June 2011 and June 2016 were identified from our institutional, prospectively maintained rectal cancer surgery database.A total of 82 patients were divided into one of three categories for BMI [obese (BMI > 27.5), overweight (23-27.5) and normal weight (18.5-23)].Clinicopathological parameters, postoperative morbidity and mid-term oncological results were compared between groups.RESULTS: In this series, 23.2% of patients (19/82) were obese, 54.9% (45/82) were overweight and 22% (18/82) were normal weight.There were no conversions and 30-day mortality, and R0 resection was achieved in 81 patients (98.8%).In addition to tumor size, no significant differences in clinicopathological features were noted between the groups.Although operating time was significantly increased in obese group, higher BMI did not compromise the safety and efficacy of Lap-ISR.However, obese patients were at increased risk for overall postoperative morbidity, including Dindo Ⅲ-ⅣV complications and anastomotic complications, specifically, mucosa ischemia.After a median follow-up of 21 mo (range, 3-61 mo), the rate of indefinite/definite proximal diversion was higher in heavier patients, but the difference did not achieve statically significance.Furthermore, the categories of BMI influence neither the 3-year disease-free survival (DFS) nor local relapse-free survival (LFS).CONCLUSION: Obese patients undergoing Lap-ISR for ultralow rectal cancer are at increased risk for prolonged operating time and postoperative complications, but the categories of BMI may not influence mid-term oncological outcomes.