BACKGROUND This report examines the viability of the W reservoir as a reliable option for the treatment of ulcerative colitis and familial polyposis and studies W reservoir adaptation as reflected by changes in compliance and stool frequency. METHODS Since 1984, 109 patients have undergone proctocolectomy with W reservoir reconstruction. Ileal reservoir static compliance was measured in 70 and 57 patients at 2 and 12 months after ileostomy takedown and in 25 patients at 3 years. Compliance was calculated as the change in volume over change in pressure. RESULTS Twenty-four-hour stool frequency decreased from 7.3 +/- 0.2 at 2 months to 4.9 +/- 0.2 at 1 year for patients with ulcerative colitis and from 6.3 +/- 0.4 to 3.4 +/- 0.4 for patients with familial polyposis (p less than or equal to 0.05). Compliance increased from 12.7 +/- 0.6 ml/mm Hg to 14.3 +/- 0.6 ml/mm Hg between 2 months and 1 year. No significant increase in compliance occurred after 1 year. Ninety-six percent of patients were continent during the day at 12 months although 10% experienced occasional minor leakage at night. Average postoperative morbidity (for example, small-bowel obstruction, anastomotic complications) was 35%. No operative deaths, pelvic sepsis, or reservoir loss occurred. CONCLUSIONS We conclude that W ileal reservoirs (1) are an excellent option for ileal reservoir reconstruction, (2) have optimal functional and compliance properties versus lower capacity designs and straight ileoanal pull-through procedures, and (3) maintain stable compliance characteristics and functional reservoir volume after the initial year of adaptation.