We report a case of rectal diverticulum developed after stapled transanal rectal resection (STARR) procedure for obstructed defecation. A 21-year-old woman with chronic constipation was diagnosed with a rectocele at defecography. The patient underwent STARR procedure. Six months later, she presented with severe constipation requiring enemas and a worse condition than that preoperatively. Defecography and rectoscopy revealed a rectal wall diverticulum cavity with incomplete elimination of barium enema. The patient underwent transanal diverticulectomy and direct rectal wall repair. STARR procedure can produce new and difficult-to-treat complications and should be reserved for expert colorectal surgeons with proved familiarity in transanal surgery.