Endoscopic mucosal resection and surgery have been the treatments used for resection of early neoplastic colorectal lesions. However, since a few years ago the endoscopic submucosal dissection is a procedure accepted for the curative treatment of these lesions. Among the complications that can occur with this procedure, perforation is one of the most serious ones, requiring in most cases surgical management. A case is reported of a sixty-year-old male patient diagnosed with an extensive flat colorectal polyp, who underwent an endoscopic submucosal dissection, with the subsequent complications of a perforation with subcutaneous emphysema and extra peritoneal air. In conjunction with the surgical team, a decision was made to apply a conservative medical treatment based on suspension of the oral intake and antibiotic therapy, yielding good clinical and imaging evolution.