A 65-year-old man with bloody stools was diagnosed with sigmoid colon cancer on colonoscopy. A preoperative barium enema and a computed tomography colonography scan showed a medial displacement of his descending colon. The preoperative clinical diagnosis was stage cT1 colon cancer, N0, M0, cStage I . Laparoscopic sigmoidectomy was performed. We found adhesions between the descending colon mesentery and the pelvic wall, and noted that the descending colon was not fused with the retroperitoneum and was shifted to the midline. The patient was diagnosed with persistent descending mesocolon (PDM). PDM is a congenital anomaly of fixation resulting from the failure of the descending colon mesentery to fuse with the parietal peritoneum. Anatomical findings should have been noted during the operation, including the fact that the descending colon artery, sigmoid colon artery, and superior rectal artery often branch radially from the inferior mesenteric artery. It is important to understand the anatomical characteristics of PDM and to improve on existing surgical procedures to ensure safe laparoscopic surgery for these patients.