目的　研究直肠癌远端壁内扩散的规律 ,为临床保肛手术提供依据。　方法　收集广州中山医科大学肿瘤医院 1996年 8月～ 1997年 10月间直肠癌手术标本 98例 ,制成大切片 ,在显微镜下观察直肠癌的远端壁内扩散 ,运用等比回缩规律 ,得出活体情况下的远端壁内扩散长度。结果98例标本中 ,48例发生远端壁内扩散 ,最短 0 1cm ,最长 2 5cm ,其中 <0 5cm者 37例 ,≥ 0 5cm且 <1 0cm者 6例 ,≥ 1 0cm者 5例。从大切片上可以观察到肿瘤发生直接侵袭、神经侵袭、淋巴侵袭和血管侵袭。远端壁内扩散可同时或分别沿黏膜层、黏膜下层、内环肌层、外纵肌层和浆膜层进行。结论　直肠癌远端壁内扩散范围大多在 0 5cm以内 ,扩散≥ 1cm的很少。临床保肛手术远切缘≥3cm比较安全。 Objective To study the regularity of diffusion in the distal wall of rectal cancer and provide evidence for clinical sphincter preserving surgery. METHODS: A total of 98 rectal cancer surgical specimens from August 1996 to October 1997 were collected from Cancer Hospital of Sun Yat-Sen University of Medical Sciences. Large sections were made. The distal wall of rectal cancer was observed under a microscope and the pattern of receding was used. Derive the length of the distal wall diffusion in the living body. [Results] Of the 98 specimens, 48 ​​cases had distal intramural spread, the shortest was 0 1cm, the longest was 25cm, 37 cases were <0 5cm, 6 cases were ≥ 0 5cm and <10cm, 5 cases were ≥ 10cm. Direct invasion, nerve invasion, lymphatic invasion and vascular invasion can be observed from large sections. The distal wall diffusion can be performed simultaneously or separately along the mucosa, submucosa, inner muscularis, outer longitudinal muscle and serosa. Conclusion The diffusion range of the distal wall of rectal cancer is mostly within 0 5cm, and diffusion is less than 1cm. Clinical sphincter preservation surgery is more safe than the distal margin of ≥3cm.