During the investigation, started in 1959, of Swedish families with hereditary adenomatosis of the colon and rectum (ACR), 68 affected, but symptom-free, individuals were detected and referred for surgical treatment. In all of them major surgery was performed, total proctocolectomy and ileostomy (PCI) in 10 cases, colectomy with ileorectal anastomosis (IRA) in 58. The surgical mortality was 4.4%. Six patients had cancer at the time of operation, and another 2 patients were operated on for colonic cancer many years prior to the diagnosis of ACR. One of those 8 patients died from metastases. Primary malignant kidney tumour was responsible for the only additional late death in this group. In a preceding paper the primary and long-term results after surgery in a group of patients who presented with symptoms, the propositi group, were reported in detail. In this group cancer was found in 48 patients, 16 of whom died from metastases. The most suitable time for operation, and the choice of operative method are discussed. The need for future supervision of affected families is stressed, and the arrangement of follow-up is outlined.