A targeted review for the colorectal surgeon on managing Deep Infiltrating Endometriosis (DIE). The episode highlights the diagnostic delay (7–12 years) and the critical "negative sliding sign" on physical exam. We navigate the surgical decision tree—shave vs. disc excision vs. segmental resection—based on the size and depth of the lesion. Also covered is the "systemic disease" theory suggesting immune dysfunction, and why colonoscopy often fails to diagnose this "outside-in" pathology.