The clinical features and outcome of 70 patients treated for toxic megacolon between 1970 and 1984 in five university-affiliated hospitals were determined. There were 35 women and 35 men with a mean age of 39 +/- 0.2 years. Toxic megacolon occurred at the initial episode of colitis in 43 patients (61 percent). Only five patients had a specific colitis: salmonellosis, two; ischemic, two; and pseudomembranous, one. Of the 65 remaining patients with nonspecific colitis, six had to be operated on without delay because of peritonitis. In the remaining 59 patients, toxic megacolon was cured with intensive medical management in nine (15 percent), improved temporarily in 14 (24 percent), and remained unchanged in 36 (61 percent). The postoperative mortality rate was 11 percent for all patients (6/56), 4 percent for patients without perforation (2/50) compared with 27 percent for patients with perforation (4/15). None of the patients who underwent surgery within five days of medical treatment died. When toxic megacolon was complicated by hemorrhage (nine patients) or peritonitis (eight patients), the mortality rate increased to 33 percent and 27 percent, respectively. A one-stage proctocolectomy was performed in 19 patients (32 percent). Of 32 patients in whom the rectum was retained, successful restoration of continuity was possible in only seven (22 percent) within 12 months after surgery. In well-selected patients, a plea is made for rectal preservation to offer an alternative to permanent ileostomy.