We assessed urinary telomerase activity in bladder cancer patients to provide additional information for monitoring after transurethral resection (TUR). Urinary telomerase activity was detected in 22/26 (84.6%) patients with known bladder tumor before TUR. Ten of 11 patients who were available for sequential follow-up examination had urinary telomerase activity before TUR. In 4 of the 10 patients, urinary telomerase activity disappeared following TUR with or without adjuvant intravesical therapy. Three of the remaining 6 patients had recurrent bladder tumors within three months after TUR. Urinary telomerase activity analysis from patients after TUR provides important information on microscopic recurrent bladder cancer.