Thirteen cases of emergency left colon resection with primary anastomosis are presented. Production of an empty bowel and use of parenteral hyperalimentation, to delay intake until healing is evidenced by bowel function, are absolutely necessary, The "elective environment," assuring primary healing of the left colon anastomosis, consists of several factors: an empty decompressed bowel with adequate lumen, an antibiotic-depressed colon bacterial flora, assured blood supply, healthy bowel wall, and absence of anastomotic tension. The importance of not extraperitonealizing the anastomosis and the danger of long-term drains are emphasized.