Twelve patients with end-stage interstitial cystitis and intractable symptoms resistant to conservative measures underwent supratrigonal cystectomy and colocystoplasty, comprising 7 right colocystoplasties and 5 open-loop sigmoidocystoplasties. Mean follow-up was 4.7 years. Ten patients had complete relief of pain and a decrease in frequency, while 2 patients required cystectomy and urinary diversion because of persistent symptoms or infection and incontinence. Bladder function was evaluated urodynamically in 11 patients. The bladder capacities in the right colocystoplasties were between 325 and 800 ml (mean 495), compared with 180 and 500 ml (mean 345) in the sigmoideocystoplasties. Two patients suffered from mild urge incontinence. All the patients retained their sensation of bladder fullness and voided without difficulty. In only 3 cases was a procedure needed to lower the bladder outflow tract resistance. Most patients did not need long-term antibiotics. No impairment in renal function was noted. In view of the good results achieved colocystoplasty can be recommended more often for the treatment of interstitial cystitis, detubularized right colocystoplasty being the operation of choice.