BACKGROUND : At the severe end of the idiopathic constipation spectrum exist patients with chronic idiopathic constipation associated with an enormous megarectosigmoid, among whom few require surgery. We performed transanal proximal rectosigmoidectomy, involving preservation of a 5 cm rectal reservoir, to ameliorate inconsistent and unpredictable outcomes and fecal incontinence occurring in some patients operated on with other techniques. METHODS : We retrospectively observed patients with chronic idiopathic constipation with megarectosigmoid who underwent transanal proximal rectosigmoidectomy during July 2017-May 2018. We analyzed sex, age, operation indication, complications, functional outcome, and time of follow-up. We statistically compared the dosage of laxative before and after the procedure. RESULTS : Thirteen patients were included in the study. Median age during surgery was 8 years. In 9 cases, the indication for surgery was chronic intake of a daily high dose of Senna with failed weaning trials, and 4 had persistent fecal impaction with laxative-intolerance and refusal of rectal enemas. No intra/postoperative complications occurred. Currently, all 13 patients have daily voluntary bowel movements and no fecal accidents. Laxative dosage was significantly reduced (p = 0.007). Follow-up ranged 6-16 months. CONCLUSIONS : Preliminary results suggest transanal proximal rectosigmoidectomy as an adequate alternative for patients requiring surgery for chronic idiopathic constipation with megarectosigmoid. METHODS : Clinical research. METHODS : Level III.